IMHO there is no good ending for Astarion/Tav. The epilogue is done very poorly, it was either rushed and left unfinished or if it was designed that way then its just outright bad writing. It needs a lot of things clarified, more clear direction as to where they as a couple go from that point. It's really hard to say as the game has so many bugs as of right now that we all maybe missing some content, like with Minthara that just doesn't trigger for some reason.
