Well, in the 6th patch, Astarion invites the mind flayer to enter into an alliance, and in the epilogue a scene occurs, like in the romance with the ascended Astarion, I don’t know if this is a mistake. And if you want to eat Astarion’s brain, the narrator says that love comes from Astarion. I checked it myself. While the spawn of Astarion only feels friendship. So despite Tav's unpleasant appearance, Ascended Astarion loves Tav. Unless it's a patch bug.
The mind flayer alliance has already been there before patch 6. He's totally disgusted with tentacles. Just because he still has lingering feelings for the Tav he knew, doesn't mean he wants to be in a romantic relationship with a soulless monster who has Tav's memories. The epilogue basicly calls him a smooth brain, yet he has the most brain cells to realise the old Tav is gone forever and doesn't hold on to the pretence of a romance.
The love line has been there since patch 5, I've posted a link to a short with it in the improvements thread a day before the Gale/AAstarion kneeling kiss was revealed by Larian. I had a feeling something would go wrong in patch 6.
