Yeah - I also saw a pretty big change in expression for Astarion if you choose the "I just want fun, that's it" as opposed to the first option and thought that was interesting. I'm not sure whether that's intended or not, but I'd think it is? The facial expressions in this game so far are very on point, imo.
I was also thinking along the lines that it'd make sense for him to not want to commit to anyone, given that he's just reclaimed his freedom, but he does also ask people if they "have loves waiting for them" in Baldur's Gate during a banter, which might mean the concept isn't unthinkable to him? I'm not sure.

Also, from what I've seen, the "city is full of sweethearts" banter can also be him answering "no sweethearts, no. I prefer them savoury" to which Shadowheart replies "this is what I get for trying to strike up conversation". I don't even know why this changes, though, but I thought it was interesting that they put it in there.

I'm really excited to see how Gale's romance plays out, too, although it's a bit too fast paced for my liking, since (as it is now, at least) you have to get the weave scene pretty early on to trigger the party one, and out of all the romances, his feels the most committed despite him having feelings for someone else. Which means you kind of create this romantic bond with him early on, as opposed to the others, who might throw in a flirty line or two but nothing else until the party happens (maybe Wyll has another scene too, but he's so buggy for me, I can never seem to trigger them). I definitely like his romance so far, but I'd wish they'd spread his scenes out a bit more, I guess.

Shadowheart seems like someone who's had more casual relationships so far, at least judging from some of her dialogue and banter, but it seems like many think she's a guaranteed monogamous option. Probably because she only wants some wine and a chat during the party, unlike....everyone else

I agree that Lae'zel feels very refreshing, though I'd understand that people would want their player-character and her to form a deeper connection.