Well, he was a monster (vampire spawn) to begin with, yet you can "fix" him so to speak if he stays a spawn.
I'm not a DnD person, I've no knowledge of the lore and all the nuances of it. I'm going by what the game shows us is possible. According to Raphael a vampire ascendant is a different new kind of "animal". He says that all the arousals of men will return to him, the appetites of men, he'll feel no hunger and fear no sun, yet all his vampiric powers will be increased. He will be a LIVING vampire that is according to Raphael. So it is safe to assume that an ability to feel love/passion/anger/jealousy etc could potentially return to him.
And even if feelings are not involved where is the common sense, did he become stupid all of a sudden to set aside his best most loyal ally? After going through all the trouble of getting you on his side? He says it himself that he is still vulnerable, not in control of his new powers, so why would anyone do a such a stupid thing of throwing away your "partner in crimes" who can and already did protect you and stood by your side? I guess common sense is not common in games
And if you play Astarion origin you can ascend and be all goody if you chose to. You can have a love interest and care for her. Kind of inconsistent...
