i am totally open! at the top of my head if he's the louse type i can think of some sort medieval style rachel/ross dynamic where in their past they were living together and he cheated and she threw all of his things out of the house and set them on fire but he still claims they were on a break and it's still something they disagree on to this day, but they have a friendship/fondness for each other that's grown over time? i just thought of that now i'm not committed to it at all if you want to go a different route