This is one of the hardest lessons in life: betrayal. After trusting, confiding, sharing... just like plunging a knife deep deep down.

Just my take. First you should seriously think whether you still want to be with him. Then ask *him* whether he still wants to be with you. If the answer is yes, on both counts, then you will *both* need to move on, beyond the hurt (for you). Not easy but if both are consciously, and wholeheartedly, making an effort to make it work then there is no reason why it shouldn't. But it will probably take time.

You say he is seeing a psychologist, this is good. But is it a counselling couples thingy? Because it woud help if both of you saw someone so as to work the issues (him - concerning his 'screwed up past' as you say; and you - with the hurt, learning to trust him again, betrayal issue).