"he said he knew I'd probably never forgive him or believe anything he said"
Tell him..."don't you dare presume to know what I think or will do".
"Would a man admitting infidelity beg to come back into the M right away do you think?"
Yep it happens all the time. Imagine a child who gets caught with their hand in the cookie jar. First thing they'll deny, next they'll argue back, then in the end they'll cry and apologize profusely. He's saying that because he's caught up in the emotion of it all and maybe he's afraid of the OW's boyfriend beating him up.
Personally, I would tell the boyfriend so that he knows what kind of woman he's going out with. Imagine if they get married and have kids and she keeps up this behavior. Those kids and he will be absolutely miserable. Let him have the choice on whether or not he should be with her.
"He said he hates himself,"
blah blah blah. All lip service. What did he say he would do to make things right? He's just showing regret and not remorse. Regret is saying that he's sorry he got caught (very self-centered) remorse is when they UNDERSTAND the damage they've done and do things to make things right with you (spouse-centered).
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.