Hi Nowwhat74,
I'm going to buck the trend and say to lay your cards on the table as soon as possible. During plan A, she's continuously re-evaluating both relationships. Each day that passes, if she has resentment and you don't address it, or you're angry, or silent, when she needs love, then she's not getting filled up with the love from you she needs, and that's the entire point of plan A. Sooner or later she'll realize the OM is a jerk, and she'll realize it sooner if she sees you fulfilling her ENs better, right away. Others will claim that this is enabling her to continue the affair, but look at the reasons she had it in the first place. You'll find that if she's still missing what she needs, the A will continue, won't it?
In my case so far, the WS has responded well to openness and love, and didn't respond well at all to the initial shock, anger about it, demands to try to curb it, or not admitting any fault in it occurring. Yes, a lot of it was her decision and it was the wrong decision. But I'm not blameless either. Admitting my faults, and giving her love seems to have had a big effect on her. Telling her how much it hurts and to not do it again, rather than anger or demands, has gone a long way to having the W back rather than the WS. The WS attitude still shows up occasionally, but only breifly because I'm not responding to her in ways that enabled the WS to feel justified to continue an A and she seems to revert back to the W when she sees I'm not responding like I used to.
Everyone is different, BS's and WS's, do what you think would work best. Try things, see what works best for you.
God bless,
CS