I had exactly the same impression about Astarion's romance, as if I were talking to 2 different people. The biggest WTF moment was the final conversation (after the dock scene). It seemed to me that during the conversation at the cemetery, Tav and Astarion reassured each other of their feelings. During the final conversation, Astarion's surprise that Tav wanted to continue the relationship and his question if that's what Tav wanted was a complete mismatch.

BG III - group on Flickr