Ambivalent, You've forgotten the most important reason all of this is happening...he is in mlc and they do stupid things. They aren't always rational, they are experimenting, they are seeking out things that they may have never done as teenagers. They are trying to play catch up and go back and do things one more time. Unfortunately, we all know you can't go back in time, but they think they can.
Bottom line...this crisis isn't about you, your family or your marriage...it is about HIM and what he needs to do to find the "self" that was never allowed to grow as a child.
Listen, girlfriend, you've done nothing wrong here. No matter what you did or didn't do, he would still have had a crisis. Heck, he could have been a monk or a priest or married to someone else or even single and trust me, he would have had a crisis. Bottom line, he's got to focus on himself and yes, it's "me time" in his world.
Okay, so you think you screwed up in the last 24-48 hours. Know what? We all have done it. My goodness, I can laugh now at the things I said and did when I discovered the whole basket of antics my little Rip Van Winkle had been into. What you need to do is understand that you are human and have a heart of gold that has been stabbed w/pain because of the knowledge you have learned. If you hadn't reacted the way you did I would have most certainly thought something was seriously wrong w/you. The reaction you had was a very normal one.
Nothing is going to be resolved w/him for a long time because he's in crisis. You have to learn to accept him for who he is today because he's a kid out there exploring a world that he was never allowed to explore at a very young age. Yes, it hurts, but you've got to let him go. You can leave the door ajar and love him unconditionally from afar, but you will not make him see reason once he's boarded the Mother Ship.
You care because you love this man. You care because you've spent a long time w/him in a marriage that had its ups and downs, but no marriage is perfect and trust me, if he hadn't been happy, he would have left a very long time ago. So, don't for one minute think you or the relationship are at fault. I think you need to read a thread that I created many many years ago on my thoughts of why they run away. I'm going to post the link here and I want you to read it. I had a front row seat to observing and being friends w/a very off the wall mlcer and what I heard and saw was enough to make me realize just how fragile these people are. I can honestly tell you it was a very sad, but enlightening journey for me.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.