There is NO question that you are truly, a loving and compassionate woman. As I read your posts and "hear" the pain of your daily existance with him coming acrossed through your words, my heart aches for YOU and for HIM.
He is a very 'sick' man. He's sick clear down to his soul. Believe me, he KNOWS how sick he is...and he keeps telling you that he knows it, in his own twisted sort of way.
He constantly berates himself as well as you and his sons, but it's NOT because the three of you deserve it, it's because he truly believes that HE doesn't deserve the three of you. He tries so hard to push the three of you away in order to prove to himself that HE'S NO GOOD.
The OW is someone on his level, she is just as 'sick' as he is...there's no one there he has to measure himself against and see himself as less than them. In fact, his attraction to her is that SHE is more pathetic to him than HE IS to himself...so with her, he can feel a twisted sense of superiority.
I'm sure your H has his job in jeopardy. I'm quite sure his co-workers and supervisors are fully aware of his erratic behavior. And while you stand by him...they won't feel that same obligation and he'll eventually be fired or asked to commit himself to rehabilitation because he is becoming a 'risk' and a "liability" to the company that employs him.
He's spiraling Cath...his 'bottom' is just up ahead.
Hang in there continuing to do what's best for you and your S. I really don't think it'll be much longer before your H goes into crisis mode and he'll either sink or swim from that point on.
T2