Is he still into her? is she still into him?

First of all, why are you having three kids with someone you are not married to?

That's waayyy out of control. I could see one, but by two there needs to be a commitment to family and love.

Secondly, why is she now your friend? And are you really ok with them being around each other again, or was it that you just wanted to be "cool" and act like it wasn't a big deal for you?

If you don't want her around, tell him and her so. He owes you respect to say the least, and if it bothers you that much, he needs to honor your wishes before his own. That same goes for you honoring him, but in this case your feelings need to be cared for, and his wanting to be friendly with someone takes a backseat to that, or at least should.

I don't know what you're beliefs are, but the two of you need to have a long conversation about commitment and what it really means. Especially since it's not just the two of you that will be affected by what goes on. And in the end, those three kids need to come before everything else. Even before the two of you.

There is prob nothing to this, I am in a situation that one of my close friends is dating my ex, there are no feelings between us and all is going well, this maybe the case here. Don't worry about it.

ummmmm he might no be cheating on you my ex did that all the time he didn't cheat on me you should relax and ask him or her bout it if you find out they lie to you about it there not ur real friends