I think it suggests that they were once genuine allies before he enthralled her, and that he’s mourning more than just her passing, but also the deterioration of their relationship.
When I listen to him talk, I get the impression that he is satisfied with the post-stroke situation (especially considering Descent into Avernus).
"Manipulation or not, we need each other. My relationship with Belynne was similar in this regard. Though - less dramatic."
And being a bit hard to him triggers a threat:
"Player: I really don't care what your relationship with her was like.
Emperor: And yet you emulate it so well"
I can definitely see where the relationship feels complete for you and I know a lot of players feel the same. I'm not going to comment on Decent into Avernus since I haven't played it, but satisfied or not with how his relationship was with Belynne post stroke, there's still textual clues that she was not his thrall from day one. While I'm under the impression that he's mourning more than her passing, even if he isn't, my original post was that she was more to him than a means to an end, and I think that's pretty clear in this scene even among the various dialogue choices.
As far as that strange comment from Swen that The Emperor “does not have that level of emotion,” we actually feel his fear regarding the Elder Brain
Mind flayers can simulate emotions in the brain of other beings, the dying one on the beach compels us to love him and makes us perfectly happy for the first time in our life while he is killing us.
As far as him simulating emotions in the pc, I highly doubt that's what's happening here because the game has always been explicit whenever something like that is happening. It's made very clear through the narration that the illithid "forcing you to love it" is manipulating your emotions, and your given the opportunity to react accordingly. In the scene with Haarlep if you choose to play the "game" he's proposing, again the narration is very clear that he's manipulating your emotions and your will. The player has to make skill checks to break free from this. The dubious nature of your consent in this scene is made quite explicit. Another example is the astral tadpole. We know that tadpoles communicate with and influence one another, and that influence is made explicit when you have to make a wisdom save to reject it. For The Emperor to simulate emotions in the pc without any indication from the narration that that's what he's doing, no skill checks or anything, I see no evidence to suggest that's what going on. During the romance scene the Narrator will tell you specifically that you're feeling what he's feeling and there are multiple times to change your mind about going forward (just like in other romance interactions), and if you do change your mind, he says that he understands and moves on.
If the pc romances him, we literally feel that he cares for the pc, and in some interactions of this scene he’ll tell the pc that he enjoys their mind, and refers to their relationship as a bond of love.
Two options here: he tells how rational we are and don't need to be coddled (astral tadpole used) or how much he enjoys our mind. But it's the same tactic when we comfort him in the dream about Stelmane; if the player is not half-illithid, then he adds the sentence: "You have shown me great empathy. We are closer now, close enough - I hope - that I can ask you to reconsider your position regarding your physical form."
If he is humanized, then he shows feelings. It's a breach he can exploit.
"Player: You really don't sound like a mind flayer.
Emperor: I have learned to adapt my methods to your needs."
The Emperor asking the player to reconsider their physical form, while also expressing care and enjoyment of their company are not mutually exclusive. He can both care about the pc and also want them to embrace transformation. Transformation is something that he never forces on the pc. As far as the line about adapting methods, I do completely understand where that can be interpreted as an admission of insincerity, but that's not the only interpretation that I think a player can come to in good faith. In the missives there's a bit of a theme of how The Emperor communicates as an illithid vs. the method of communication through letter writing, so adapting his methods doesn't necessarily mean "acting human" in the sense of faking emotions or having no sincerity. I do admit that I think this line is left intentionally vague to make the player question exactly what you bring up.
There’s an option to tell him to think bigger, at which point he’ll say to them “Have I ever told you how much I enjoy you? Lead the way…
True but in his letter you can see he is the one in charge and even tells: "Make merry with your former allies, for we may yet have need of them. Keep them close, and wait for my word."
(That was exactly what I was worried about before the epilogue patch. There was no way he would have really let someone else make decisions and follow another plan.)
So there are four possible missives, and I had to reread them because it's been a little while.
If you don't transform, The Emperor calls you an ally, thanks you for the invite, and wants to continue to be allies as he rebuilds his old life.
If you transform but choose not to join him and instead "do some good" in the world, he sounds very dejected in his letter, almost petty about your choice. He expresses how he wants you to embrace your "evolution" in time and ends it by saying "and when that time comes, call on me. My mind will be ever open to you."
If you transform and join him in rebuilding The Knights of The Shield, his letter is about setting up the new headquarters and his language is explicit that he now sees it as not his but "ours." He also talks about finding comfort in your allies but also to not hold on to the past.
If you transform and tell him that you need to think bigger and achieve more, this is where you get the reference of contacts (possible thralls, though I don't know how that would work since they're in a different city entirely). This is also where you find the line: "Make merry with your former allies, for we may yet have need of them. Keep them close, and wait for my word." However, the missive in its entirety reads like a partnership. I don't see anything in the letter that indicates to me that he's calling all the shots. He's out making business connections while you're at a celebration and it's basically just an update on that. I think it's worth mentioning that it's the pc's idea to go bigger because you're both mind flayers, which then leads to this massive alliance of black market syndicates.
“Perhaps you are unique among illithid-kind. Perhaps you will retain enough of who you are to resist your nature. A rogue mind flayer. Like The Emperor.”
This is a pretty straightforward acknowledgement that The Emperor does have the capacity for relationships beyond mere tools for his use.
Not convinced from what the game shows. He said in one of the first dream: "[…] gather many allies to aid your strength. Use them how you will", the essay about moral in his hideout ; the fact he doesn't express interest for Omeluum, preferring to commune with an other criminal mind flayer in one ending, and it seems he even makes more thralls: "I have established 'contacts' in Calimshan - they answer wholly to me."
In an other letter we get: "Make what memories you must tonight to ease your passage into the future. In time, those you cherish so dearly will become just that - fond memories, and nothing more. And when that time comes, call on me."
I don't see him interested in remaining/becoming a lover while our feelings decay, just as he doesn't retain us when we speak about hiding in the Underdark. He doesn't want to babysit us or build a friendly relationship. I could have missed something, but I'm pretty sure all his intentions revolve around business (and world domination).
I addressed most of this above, but I'll add that I don't think it's mutually exclusive for him to be interested in business dealings and also his relationship with mind flayer Tav since the two missives you mention here are from a transformation ending.
The quote you mention from the first dream, I admit in all my play throughs I have never seen that one. I know at the end of act 2 he tells you to gather allies to your cause, but the line above is one I haven't seen. I also haven't seen any dialogue with him about going to the Underdark. I know that's something you can propose to Astarion in one of romance endings, but I've never seen that dialogue with The Emperor.
I don't think his apparent lack of interest in Omeluum is relevant here. You meet Omeluum long before knowing the Dream Guardian is The Emperor, so I don't know why he would comment on him then. As far as saving him later, I don't think it's relevant to The Emperor. He doesn't comment on much, so I don't think it says much that he doesn't comment on Omeluum. He communes with another criminal because it's the ending where he and Tav become these powerful criminals. The Emperor is not good aligned. I know some will argue that he's neutral, however, I personally disagree. I believe he's evil, but that doesn't mean that he has no nuance.
If you save the Grove, he’ll even compliment you on your leadership.
He supports our action, whatever it may be.
"For what it's worth, you made the right choice. If we don't accomplish our goals, none of this matters. Not their fate, not anyone's"
"It's a good thing you decided to infiltrate the cultists rather than fight them. The Absolute has already mustered an impressive army, and its forces still grow"
This is true. He does support our actions whatever they may be because of everything that's at stake, but he admires leadership and expresses that when the pc shows leadership skills. The player can make of that what they will.
But, let’s just say you have romanced The Emperor, but the twist is that you are merely a means to an end. Well, that’s not clearly laid out either.
He refuses to leave with the humanoid he bonded with.
When companions randomly express their joy for having saved the city, he says: "It makes little difference to me. I did what I had to to secure my freedom."
Romance aside, we should be able to create a connection with him by being more Illithid, but it's not even the case. All the little nice sentences are reserved only for the group leader who didn't commune with the astral tadpole.
It's just my theory but I believe after tried everything to convince us he finally came half-naked because his outfit was intimidating and he needed us not to be afraid of what he wanted us to become.
Or just as an emotional grip. Correct me if I'm wrong, but I think he refers to it three times: during the interaction with the portrayal of Stelmane (giving a compliment by extension), for returning to the House with the Hammer, and to acquire the stones if we are reluctant to trust him.
His romance could be incomplete; but for me, everything is coherent by far, there's just no romance at all.
In the ending he'll leave out of a matter of safety. The city was practically destroyed by an elder brain and its illithid thralls, so getting out of there is important. That aside, the solo ending in which he confesses that you've become important to him I think is really telling. The Emperor has an implicit and explicit desire for compatibility, and I can completely see where he can care about the pc and bond with them, but have doubts about the territory of a relationship with a non illithid. If there were to ever be a more fleshed out romance with The Emperor, I would love to see this kind of dynamic addressed. He believes being an illithid is an evolution, yet he's bonded with a non illithid and that's some really interesting territory to explore.
I'm not entirely sure what you mean by "all the little nice sentences are reserved only for the group leader who didn't commune with the astral tadpole" as he's quite complimentary when you take the astral tadpole. I don't agree with the theory about him showing himself half naked because his outfit is intimidating. I don't recall him ever mentioning his outfit. He's half naked in the romance scene because for him, you getting the githyanki out of his home and him sharing his personal artifacts with you is a bonding moment for him. I'm also not entirely sure what you mean by the three references. He tries to persuade the pc to take the astral tadpole and makes reassurances about changes to their physical form. If you offer to become a mind flayer, he'll tell you what that means and asks you if you really want that.
I know I mentioned this above, but I think it's worth saying again that I don't think The Emperor is a good-aligned character, and I don't think he needs to be to fill a romantic role in the story. I said in my original post that the pc is a means to an end but not only a means to an end. You can even have this exact dialogue exchange before the romance scene if you tell him that you sound like an experiment to him. It's a common trope for relationships of utility to turn romantic, so this is pretty well-worn territory from a storytelling perspective. One of the things I find interesting about a romance with The Emperor is that he ticks a lot of the boxes for what you tend to find in monster romances and romances in which the romantic lead is a villain or some kid of predator (like a vampire for example). There's a narrative tension between the characters where one is considered weaker. However, very often the "weaker" partner in this dynamic becomes stronger through this relationship and whatever possible power or danger the "stronger" partner has is secondary to their bond and feelings for their partner. The writers laid a good foundation for this kind of dynamic in a romance with The Emperor, but again, it just feels incomplete.
