Hi Jennifer,
I know it's a cliche, but have you talked with your new partner about your fears and anxiety? If not, I'd say it'd do you the world of good.
Aside from this, keep reminding yourself that no two situations and relationships are the same. It's a very hard one to overcome, when a partner has an affair. That guy had no right to do what he did. May I suggest you write down all your feelings towards the bloke that hurt you. Just pour it all out on paper. If you feel up to it, confront him. I don't mean go over to his place with guns blazing or anything. Just tell him something like "hey, you really hurt me and I want you to see the impact your actions have made on me and my new partner." Explain that you want to be at peace with him and the situation, so you can put it in the past. Explain doing this is part of it. I'm guessing you have some things that have been left unsaid for a long time. Try to remember, it's over and you're now in a different relationship with different circumstances.
I know it's hard to feel good when all the while you're feeling susspcious. Like as soon as you let your guard down, you're going to get burned again. Bringing things out in the open will help restore your trust tremendously. :)
