futureunknown. While an affair is going on what are you doing in the marriage? Seriously? Remove yourself from it. Set the boundary and enforce it. Your choice is to be in a marriage with only the two of you. Her choice is accept this or leave. Not both. Respect yourself. You made your mistakes. Let her go make her mistakes.
cutterbug-
I did remove myself from the marriage for quite a while, and I had resigned myself to D, but as my W's affair died down she started to reach out to me, just as robx describes. In my case, OM is VERY far away, so that blurred the situation a bit for me. Our M was very broken long before the affair, so I decided to ignore the affair for a little while and just work to rebuild my R with my W. My belief was that if my W had only our history to look back on, she would never decide to come back. I had been working on myself all year, as had she, and I was curious as to how we would now interact. I was surprised how strong the connection was between us still, and so was she. It was only after I found myself getting pulled back in that I set my boundary and told her I can't continue to see her while she is still involved with OM. She hasn't yet responded.
This is exactly the kind of clarification I was looking for from robx. If an affair requires an absolute complete block to all interaction with the WAS, then his advice doesn't apply to the majority of situations here, because an OP is involved most of the time.