I'd like to second this. I usually, meaning twice, chose to ascend. Granted, I've only played through ToB three times, due to the lack of romances that are done for it, but leaving my love behind always bugged me.
If I'm good, it always seemed like a cop out to not take this great chance to do good on a universal scale. But, I sure as heck don't want to leave my beloved Viconia behind. That said, I wouldn't want to see bringing one's love with them just in the epilogue. Rather, I'd like to see it sort or spread throughout ToB, maybe in the form of dialogues with your romance, maybe chances to release some of your divine essence into the love interest. This would probably be represented by permanent xp or level loss. That way, it's not just a one time decision with no repercussions; it's something you have to really consider. And of course, then there's the risk of the signifigant other contracting some to the taint, and you helping them deal with it. Or not. That could be random, or influenced by something you do. Or, give the player the choice of making sure that the taint stays with them when they give up some of their power. Of course, if they choose to do it the noble way, then the Slayer may manifest on its own again since they've less essence to control it with. Just an idea.