She’s a midwit like Tarl but she does come from a much better family than he does. Also, she did break up with him after they met in person for the first time and she saw how he lived in Rutland.
Once she went back home and the nightmare that is Castle Warwick faded, he was able to reel her back in. I Imagine, like a lot of women, she thought she could change him and take him out of that dumpster fire and she did for a while. He hit peak performance while in Amsterdam.
But Tarl is Appalachian hill-billy gutter trash. He was never going to be able to maintain a healthy lifestyle. He eventually went back to his old abusive ways getting drunk and cheating on Liz with his succubus.