I totally understand how you must feel now. It really is a lot of heartache and can cause terrible panic attacks. I know the lack of sleep and appetite all too well.
It really is not about you. Your W is incredibly selfish and absorbed in her own happiness right now. I think that when another person comes along, it not only causes their common sense to get all fuzzy, but lowers their IQ for a while. Your W is having difficulty knowing right from wrong.
Did you specifically tell your W to not introduce the kids to OM?
I ask this because I had something very similar. I insisted that my W not involve the kids in her A and she promised me she would not. But I found out from my kids otherwise. They told me that their mother was kissing the OM right in front of them and that he even kissed my daughter. My daughter thought it was neat that mommy had a boyfriend. My line was crossed by her unwise choice of including the kids in the A. I filed for a D.
I am not suggesting that you file for a D, but you do need to have some boundaries as to what life lesson is being learned by your son's now. As it stands, I am not certain if there are any consequences for poor actions on your W's part.