Krosp: I like Tarvek. He thinks like a cat.
I happen to like Tarvek too, even though Agatha is clearly going to end up with Gil. Or perhaps, because Agatha is going to end up with Gil. Tarvek has that whole internal struggle of 'all my life, the only way to survive has been to be a bad guy. Only the amoral, self-interested survive. 'Do unto others before they get a chance to do unto you.' Etc.
But inside, he wants to be good. He wants to trust. Look at his backstory with Gil. Oh sure, he says 'I wanted him for a minion.' But in reality he wanted him for a friend. Gil's betrayal still burns Tarvek on a personal level, as opposed to every other betrayal from his 'family.' It's that spark of good (and the whole bad boy thing) to which Agatha responds. And its part of what drives Tarvek to love Agatha. She is the first person he has ever met he can actually trust, when she isn't possessed by his homicidal relative.
This doesn't change the fact that Agatha and Gil are still the right couple. For one thing, Agatha could never live with the kind of moral relativism that Tarvek will never manage to totally lose.
But it will be fun if we ever get back to moving the story along.