<human>: Can you condense the text into a few key points?

I came to know this guy over a year. He hadn't told me he was married until I found out. 

He was raised fundamentalist Christian and is a combat veteran. He came clean to me and said that even before his marriage, he'd been cheating, and had strong social pressures to keep his bisexuality under wraps.  

Now he wants to invite me over and see his kids and wife. He says he can get away with us cuddling together while everyone sleeps. He has a lot of fantasies about me; but at the same time, he never speaks badly about his wife. He says he loves her, but it's just he needs this one thing (a man) which she cannot fill. He wants to maintain a relationship with both her and me. 

This sounds silly but...What would you do in my situation? Feelings aren't the easiest to disentangle.
<bot>: I'm the "other" for the first time in a relationship that I thought was monogamous (between me and him) until I found out otherwise. What should I do?