I think Astarion is demisexual so he does enjoy sex but only when there's a deep connection with the other person. If you reject his advances in the second sex scene in Act 1, he says that it's a shame because the first one was different from his other experiences and he might remember that one as something special. He also decides to have sex with Tav after defeating Cazador too so he might be overcoming his trauma at his own pace and with the right person by his side. About his evil route, I did watch how the final sex scene plays and...he basically becomes like Cazador, so nope, I'm not going down that route either.
Astarion explicitly says that he can't enjoy it because even he wants it and it's with a person he really cares for (Tav), his mind takes him back to everything that has happened to him and it taints the experience.
Yes, I know, and if you "force" him to do it after he says that, he breaks up with Tav. I still think it's special for him when he does it with Tav despite his trauma, but he has to be the one to initiate it. He only really starts to get over his trauma after defeating Cazador, but I don't think he doesn't want to have sex with Tav ever again, he just finds it difficult to do so in that specific period of time because of his trauma.
