I think your past hurts & betrayals are what's causing your problems now. But you can't judge a book by its cover. So to think your new girlfriend will do anything with your b/f is making her guilty before the crime while she is still innocent. And if you're waiting for her to become guilty, you could be missing out on a great friendship.

Stick with the therapy and take it one day at a time. And definitely don't let your imagination get the best of you.