I think if you are telling your H that you can't ML because you "feel used" you need to ask yourself what you were doing with the OM. He wasn't committed to you, was he? He was sleeping with a married woman, therefore he could not have been committed. What were his motives in sleeping with you? Your H is still your H and has suffered a huge trauma. Especially if you still have that emotional connection while ML, then I can see why he craves that.
Maybe you should call a DB coach? I am thinking of this from the betrayed spouse's perspective and I feel really badly for him. He obviously still loves you and wants to be with you, and is trying to heal. It takes a very long time to recover from something like this.
