How do you feel about cheating WITH someone?

[Gemini]

Last night, I went out to a club with my friends. We all love to dance. So this guy started dancing with me. He was pretty hot, and seemed nice and funny. We danced and flirted and kissed a little. When the club closed at 2am, we went to an all night diner for coffee and to talk some more. He asked if I was going to invite him back to my place and I told him it was awkward because I have roommates. But I said I was in the process of moving into my own place (I'm picking up the keys today!) He didn't mention his place, so I asked if he had roommates too. Then came the story.

He has a long term BF and they live together. NOT an open relationship, I asked. But the relationship is going badly and they hardly talk and don't have sex anymore and he's trying to break it off - but his BF is clingy, needy and dependent. He's trying to let him down easy. BlahBlahBlah. I was hearing it as the old, "My wife doesn't understand me" routine.

So I told him to call me when the relationship is actually over. I said I'd love to go out with him then. He didn't like that at all. Don't think I'll hear from him again lol.

But here's the thing - I make it a rule never to go out with, sleep with, etc. a guy who I know is involved with someone else. No matter what kind of line he feeds me. First of all, I don't need the drama. But also, I can't help putting myself in the BF's place and thinking how I'd feel if someone cheated on me.

My friends say I'm naive, everyone fools around. He's the one who'd be cheating, not me. I should just relax and have fun.

I'm not buying it --- but I'd really like to know how others feel about this.