Why is ex husband so mean?

If he's an Ex Husband why would you even care? and she's not playing 2nd if he's living with her now, so if this man comes back around you, and you sleep with him, then you're sealing yourself short. I'd only let him come see the kids and that's it, find yourself another man and move on with your life, seems as if he has..you don't even have to talk to him, in a way that gives him the chance to be mean to you..