Wow, sorry to hear about your son!!! I'm glad to hear he had x-rays and that everything is okay.
I agree with you about the situation being a sort of gift. Although it's very painful, it is a time for self-reflection and growth.
With regard to your son's being around OM.... Fortunately your boys are old enough that they can probably choose where they want to be (depending on the laws in your state). So if they don't want to have any contact with OM they don't have to. I would guess they probably don't want to be around him since they are old enough to realize he is partially responsible for their mom no longer being with them.
I would guess your W probably won't push for a D unless things get uncomfortable for her in some way. It would probably be easy enough for her to skirt along the way she's going now. I think this is a positive because it will help you maintain more control over the kids. And it will give you and the kids a longer time to emotionally prepare for the D if that is going to happen.
I have to share this interesting experience I had the other day. I ran into an old friend of mine. We had been neighbors and close friends when our children were babies. She has one son my daughter's age. When the kids were in around 1st grade she decided she didn't love her husband and no longer wanted to live with him or be married to him. She moved out, got a job, left her son with his dad, had a "male roomate" for a little while, and I lost touch with them... we moved. I'd hear bits and pieces about them now and then over the years, but not very much. Once about 5 years ago we did run into her and her ex at a resturant. I was kind of surprised to see them eating dinner together, but I figured they were just discussing their son or whatever...
So... here it is about 12 years later and I run into her. One thing that shocked me is she said they were not divorced. Apparently they separated, but neither of them ever got around to filing for D. She dated over the years, but she said she hadn't been dating during the last two years. The thing that surprised me is that said the last two years of her life have been very difficult she was angry with her husband not being there to emotionally support her because he recently met a woman and now has a girlfriend.
Here is this guy... his W moved out 15 years ago, he raises their son while she leaves, has some "male roomate" for awhile, dates, lives her life... and now she's angry at him for finally "having a girlfriend" and not being there for her when she needed him!??? Sheesh... and where is the center of the world???
There is no arriving, ever. It is all a continual becoming.