I agree, somehow the writers seem to have decided for us that if you choose to Ascend Astarion than your character can't possibly love him. The question of whether an Ascended Astarion can return that love is an entirely separate issue. I think it's perfectly legitimate for Tav to have fallen in love with the darker side of Astarion's character from the start, and to prefer that aspect of him. This is roleplay. Characters should be able to have any number of motives driving them, pure and otherwise.

Honestly, this is a topic I could write pages about. Astarion is just that layered.

Yes, it's clear that Tav will never be an equal in Ascended Astarion's eyes, and they will never be free from him. Neither of those things suggest to me that the relationship would be passionless. To the contrary, a lot of his comments suggest that there's a great deal of attraction.

I do love that kiss, too.