I don't understand why you're internalizing his wrongdoings. You're blaming yourself for not being able to trust when he violated your trust! Your brain is working correctly in not trusting him, but for some reason you are trying to override your brain by saying the trust issues are your problem and not his. It's like if someone killed your dog, lied about it, and then you blamed yourself for not being able to trust this person anymore. What I'm trying to say is trust your brain! It's guiding you in the tight direction. (Yeah, IMHO cheating is a COMPLETE trust breaker.)

And why are you trying to forgive someone who isn't sorry, isn't repentant, and lies, lies, lies? Is it for religious reasons? God doesn't want us to be doormats, so says my priest. Forgiveness isn't mandatory.