I think the bottom line here is either you trust what she tells you or you don’t. If you don’t think you can trust her, the relationship won’t last no matter what you do, whether she’s trustworthy or not, because the insecurity you feel will eventually drive a wedge in the relationship.

Speaking as an independent female myself, I am friends with most of my ex’s. I would not want to be with anyone that would ask that I cut one or all of them out of my life because, for one, that would basically be him telling me who I can or cannot talk to, which I would not at all appreciate, and, for two, I truly have no residual feelings for the ones that I still talk to, so there’s no reason for anyone to feel threatened by them.

If your girlfriend’s ex is trying to get her back and she is refusing, I would believe what she says. If she wanted to be with him, it’s clear that she could, but she is choosing to be with you.