I hope you don't take this the wrong way but here goes.
You my friend need to move on and right now. The sitch sounds self inflicted by you. What is the heck were you doing having sleep overs with your XW for? No excuses about wanting to be with family either, you have not detached. Want proof?
You freaked when you found out your single, XW was having out of town sleep overs. So what? You are not married and you haven't accepted the sitch. There would have been no freak out at her place if you hadn't been there in the first place. This behavior is so not DB.
Something else, it is your opinion that you are the better mate for her. Not your decision.
Oh, here is a good one. Romantic rivial, if this doesn't tell you that you are not detached nothing will. Do you really view yourself as a "romantic rival?" I bet your X doesn't?
The e-mail thing just futher solidifies your inability to detach and move on. Again, not a DB principal. In fact it is something that is advised against. Kind of hard to defend yourself against accusations of obsesive behavior when you provide her enough ammo to take you to court.
BTW, I had been with my STBXW for over 24yrs when she bailed on me. I know what it is liked to be replaced by OM. Get over it before you ruin the rest of you life.
Me 45 WAW 46 Married 23yrs D22 S18 D12 W moved out 1/12/07 Divorce Final 2/06/08