I've never been in your shoes and wouldn't presume to give you specific advice, but you sound like you're not very sure of yourself right now. I don't blame you. I wouldn't be, either, in your situation.
You will not get over it quickly if you get over it. You and he should both expect it to take a long time.
I think you're smart to assume that he's not telling you the whole truth. He's likely ashamed of what he's done and afraid of what you're going to decide in the end, and that means that even if he wants the best things for your marriage he might still hide some things. It's good that he wants to go to a counselor, but what did you think of the counselor? They're not all created equal and this forum is full of people who regret going to a marriage counselor who saw it as their job to keep a divorce amicable rather than to help save a marriage. If you're not comfortable with the counselor, don't be afraid to find one you prefer and tell your husband you want to go there. Counselors are professionals who work for you at your pleasure, no different than a roofer or a plumber.
My guess is that a week after you found out what was going on, it's perfectly normal if you're still reeling and hurt and feel like you can never forgive. I would try to concentrate on soothing yourself and doing each step in your process; try your best not to think about whether the whole process will work for now and just do the next step. And come back here and vent whenever you need to . . .
