There was nothing that made you do anything,you made the choice of your own free will.
Talk to her about it and let her know she has to stay away from her ex.
she is your ex-girlfriend so,let her date leave her
Probably the best things you can do are to stay cool, stay faithful to your girlfriend, and communicate with her. Keep building a relationship and alliance with your girlfriend. If you make it a "thing" between you and her ex, you are lost.
let him go
To say: "Just to let you know, I dated this girl before you; but we are through now"
No, just tell her that your ex wasnt the right girlfriend that she wasnt right for you.
Stare at her. Tell her. Be smart
No! Of course you shouldn't! Just because she doesn't want to hate him doesn't mean she hates you! If she wants to stay friends with her ex, you should let her. She's going out with you right!?
No If your ex-g/f is the mother, yes. If not, no.
Not if you trust her, and if you don't trust her you should be finding someone you do.
Yes.
Yes.