I think you're going to first need to take some time as GH suggests to assess how you feel about your M and what end result you want. I recently gave my H an ultimatum of sorts as well. The problem with ultimatums is this: you have to be prepared to follow through with what you have said. Otherwise you run the risk of making idle threats and your H won't take you seriously.
So you have to ask yourself if you are really prepared for things to be over. I'll go ahead and take the risk of assuming you are not. Otherwise you would not have found your way to this Web site.
I would suggest it is a good time for you to go dark. Have you read Michele's books yet. If not, get your hands on a copy of DB and DR.
It is a good sign that your H regretted going on the trip. That said, if you were to take him back immediately (that is backing down from your ultimatum) you will probably both fall back into old patterns. He will assume he can do whatever he wants without consequences (and the problems that led to his A will still exist) and you will have not take the time to understand the role you are playing in the breakup of your M and in his A.
Have you taken a hard look at the underlying problems in your M? As much as many of us don't want to admit, just because we're not the ones cheating doesn't mean we're not equally to blame. Until my H had not one A, but two, I never realized how much he meant to me and that I completely took him for granted.
