I'm always a little worried that STBX will turn jerk-y.
I worry a little about this sometimes. H and I have been nothing but civil to each other, and since he moved out he's been downright nice. But I'm always aware that I never thought he'd cheat and leave, either, so I'm vigilant about checking the bank accounts, etc. for anything suspicious. I'm ready to take care of myself if need be. But until then it's advantageous to keep playing nice.