The ‘thank you for trusting me’ line you get the morning after being turned always felt sincere to me, as opposed to one of his sweet nothings. That whole conversation reads as him finally breathing a bit easier and getting to revel in his evil plans with faith that Tav wants to share in them fully.
I also found it jarring that you can tell Jaheira in the epilogue that Ascended Astarion is the love of your life (and it’s not flagged as deception) but you can’t tell him that. Mind you, Jaheira will also tease you about having children in the same conversation without seeming to realize that two undead are probably not going to procreate.
Trust is very important to him, true. He finally stops worrying that Tav is not serious about him.
I heard that such an option exists but in my game I can only tell her that my home is with Astarion and the conversation finishes after a few of her lines. The procreation may be possible, considering he's a living vampire and he shares his power with Tav (which is also mentioned in the epilogue) so Tav might also be warm and have a heartbeat, if they're able to walk in the sun like he does.
