Just came here to say that BG2 gives you a way to cure being a vampire spawn, but others beat me to it. I was surprised this angle wasn't explored in the game. I know Astarion has been a vampire spawn for a lot longer than your love interest in BG2, but . . . We have the ingredients to at least be able to discuss a cure. We have a Lathander temple in the game (it's not Amaunator but I think Lathander absorbed Amaunator anyway), we have Cazador's heart, we have Jaheira knowing about this . . .
Edit: I mean, regardless of whether they actually put this into the game I'll just headcanon it happens afterwards. Vampires are cool and all, but it would be such a ridiculously happy ending for Astarion to be cured, walk in the sun, not be hungry, reconnect to the elven spirit, etc.
