I'm a Carolina girl too. Remember - we're really steel magnolias underneath. I'm so sorry you're going through this but you sound smart and rational and like the others said, you'll need plenty of patience too.
Your H is young for MLC but a traumatic event can set it off at any age really. He needs plenty of compassion and validation right now. Learn to say this "I'm sorry you feel this way" when he goes off and and this "I understand" when he is expressing his feelings.
Don't discuss how you feel at all - he won't hear it.
And the OW - that's the killer alright. My H shared a lot about her in the beginning, without prompting from me. I figured knowledge is power so I listened. But some will say to tell him "please do not disrespect me by talking about her." You'll just have to decide what you can handle.
Watch your finances like a hawk. If he becomes more involved with OW he'll spend like he's the king of the world and then act stupid about it if you call him on it. If you have a joint account start putting away as much as you can in your own private account.
I'll be away some over the holidays and may not be able to post much until next week. Holidays can be emotionally draining - please take care of yourself.
Me 56 H 47 Married 21 years No children Bomb & moved out 4/07 "My feelings have changed" & "I want to live by myself". Ow Bomb 8/07 H filed 6/08 D final 2/05/10