hw:
I may get slammed from others on the 4um about this, but I think this A is "serious enough" now, whatever that means, that your sons deserve 2 be told the truth. Maybe let your WW know that you need 2 tell them, and offer 2 do so with her present, so she can give them "her side of the story." Problem is, she'll want 2 be able 2 continue 2 lie 2 them, which will enable her 2 prolong her fantasy. I don't think that's fair.
In my case, my kids are older than yours. My daughter was told back in March, when I thought I was going 2 give up on our M. My son was told we were "having problems" about the same time, but he hasn't been told the whole truth, at least not by me. He's 15, but he's also a very sensitive, considerate young man, and he loves his mom very much. And so because we started doing better in about April (with some serious dips in the rollercoaster ride through July, however), I've felt it may not be necessary for him 2 know at all.
Time and the TRUTH, and love and consideration, and recognition of OUR own shortcomings as BSs when the A started... ...all these are factors in healing from infidelity. I sometimes get impatient, even now, but one thing that's stuck with me since my session with SH in late July, was when he said "So, you only just found out this year?" I had been thinking that it had been such a LONG time since D-day for me, and was impatient for some breakthrough, that it really jolted me upright when he said that, like it hadn't been all that long. Now, I realize, that because my W's A has spanned 12 years now (thought thankfully it was mostly an email EA, even now, 9 months after D-day, it hasn't been all that long. *I* have a lot of learning and healing of my own 2 do, so that I can be helpful in my W's healing. I'm willing 2 do that for a while longer, mainly because I think we're making real progress. In so doing, though, I've been surprised at how screwed up *I* have been all these years.
Growing up has been fun.