"I only found about about his past a couple of years ago, and more revelations came out as late as last week. When we met he told me he had slept with 3 women!"
Timeframe? Before or after marriage. I am assuming this means at the same time.
"I think he thinks he is unhappy because he is not being true to himself, and now the 'real' him is coming out, maybe he feels he might need to go back to that in order to be happy again?"
"I think he wants to be free again to do whatever he wants (keep getting the "I'm 38, I'll do what I want" speech)."
This is midlife crisis kind of stuff, I think. Hopefully somebody a little sharper than me will step in on that stuff.
You may now have a two front war. If he is evaluating his life right now and is unhappy (I am 39 and kind of doing the same thing) then he may be trying to regain his lost youth. Again, need somebody with more experience here. This may just be piled on top of or beside the ten years worth of sexual rejection. Take a look at my posts where I vent about having married the wrong woman etc and my situation was not as bad!