I'm inclined to agree that something short, sweet, and straight is called for that includes NM's boundaries.
I was going to suggest something like: "Treat people with honesty and integrity, figure out what you want among options consistent with that, and then quit making excuses and make the changes in your life that you need to to get it."
Whatever the response, it shouldn't play into poor little lost boy's (GAG) hands. He is fishing for NM to fix things, pet his head and tell him everything will be OK, that it is unfair to life to be so hard on her sweet baby boy, and make it OK for him to continue treating her badly while bedding her.
Anyway, let him fish. I don't think she'll take the bait
I hate to say it again, but I think his inability to take ownership of his actions and the direction of his life in any way and his self-justifications for sh*tting on NM (and OW for that matter) suggest a history of infidelity that includes a lot more than this case. He strikes me as a guy that is used to cheating, at least to a greater extent than this one A that is in the open. I think that it is the source of his true feelings of hopelessness about changing anything or finding a longlasting solution to his R with NM.
NM, of course this is just my intuition. Even more important, it doesn't mean he can't change. Indeed, if I am right, he really is trying to change this time which is why you know about the A and why he is struggling with it. And, I could certainly be wrong in any case, lol...
Hang in there and get a full life. What is up with the job and childcare? Whatever happens with SO, it is going to be a long haul to get to an R that works, either as partners or co-parents. Make your life good in the meantime.
