Damn.

Although the majority of me agrees with all of you, I have a really hard time seeing him as this mastermind who has set out to seduce me so I sleep with him. I can offer an alternate explanation, voiced by him. He has characterized himself as a person who decided to "grow up" and sacrifice excitement, etc. for a relationship, but he says he doesn't know what his rule book says when you meet someone else you have a strong connection with (presumably me). Because he actually hasn't had his cake and ate it too (this is the fact), maybe he is a confused person who is in a state of indecision and limbo. Maybe he's feeling me out/exploring this to see if a)It is worth physically cheating; and b)It is worth breaking apart a big part of his life and making a change. 

That's obviously a more optimistic interpretation...but it is kind of my read on the situation. I guess I could test it by giving him an ultimatum, and pushing him to choose one. I plan to do so if things keep escalating a bit longer...

I'm going to try to distance myself though, per you guys' advice. It is getting too intense. We're becoming too attached. And I don't see much good to come out of that, for the moment.