I think it's great that he is wanting to be so OPEN with you - and I also agree probably not the right time on b-day!!
I found, and H has confirmed this, that whenever we talk about OW he gets to feeling SO guilty that it ends up with him wanting to retreat further back into his shell. He says his guilt is sometimes so overpowering he cannot deal with it. I on the other hand have a very hard time not getting angry. I try to relax and control my feelings and say over and over 'he's here...with me...and etc' and that usually works and he only sees a calm, rational L.
Just be very sure YOU are ready to hear all the things he's gonna say about her. I thought I was, and still I think I am 'about there', but inside, where he cannot see, I still get angry feelings whenever she crosses my mind or we talk about it. Not really anger at her, because she had no clue about me, but anger at what we have lost, like you said...I thought I knew everything about him but now I find I barely know him at all.
It can be rebuilt. It takes so much patience and understanding - on both sides. Just remember (yeah, like you'd FORGET - LOL) to go SSSLLLOOOWWW. Don't get to feeling like it's not going fast enough and yous guys are not 'getting there'.
You will get there. But like I am realizing my H's A didn't happen overnight. We'd been heading down that 'something's gonna happen' road for a few years before anything ever did. It's gonna take at least that long for it to not to be such a wedge between us. I have (almost) gotten to the point where I am not obsessed with what we could have done to prevent and what we did wrong, but am still hung up on the "why he did it" and how to prevent it in the future.
I guess what I'm babbling on about here is to gear your talks towards the future; of course the past has to be 'worked out' (if not, like in my case-progress is slower...I wonder if he'll ever truly open up to me). Face the past - to both of your satisfaction, then move forward.
Like the song says "...take it easy, take it easy, don't let the sound of your own wheels drive you crazy..."
