This sounds like a disaster. Just go home and masturbate until your vibrator breaks.
I was in a somewhat similar situation when I was in school in my mid-20’s. There was a guy in my class whom I was very attracted to; the attraction seemed to be mutual, too. I was single, but he was happily married, and even though I was really attracted to him at the time, looking back I’m very glad that we didn’t do anything about it. I think I would have really regretted doing anything else.
Think about it this way; a good guy wouldn’t be shagging anyone on the side. He would end the current relationship before jumping into a new one, if the old relationship is over. A bad guy would cheat with you, but do you really want to sleep with a bad guy? If you really want to sleep with a bad guy, you can find plenty of single ones at any local bar, so no one gets hurt but you.
More practically, if you really can’t work with this guy without being in serious danger of messing around with him, look for another job. Sometimes you need to physically remove yourself from a bad situation.
I once helped someone cheat, though I didn’t realize I was doing it. I was single and at a new years eve party, where I only knew a few people. A friend of mine was crazy about a guy there, and this became a problem when he followed me around all night. By midnight, we were making out in the front yard. Jump ahead five minutes, when his girlfriend is threatening to kill me. This came as a major surprise, as I thought he was single! I felt bad for ruining her new years, and my friend was furious with me. Despite all the drama, I’m kind of glad I did it, as he was the best kisser I’ve ever laid lips on.
I’ve tried to be as gender neutral as possible because I think that does affect perception of the situation.
I am very surprised that most people assume I am a woman.
I word most of my posts in gender neutral tones as well. You said " I would for one like to be a very sexual, devil-may-care, NAUGHTY person. Just once." Well, who doesn’t? If you haven’t lived your life up until now like that, chances are you won’t take much away from a sexual encounter with this person that leaves you feeling good about yourself inside.
You are still discovering who you are and what you’re about. Most of us still are. I live my live by several mottos, one of which is “No Regrets”. Ask yourself this: Would you regret not shagging this person more or less than the fallout of having casual sex with them (fallout being your conscience, the other person’s conscience, their parterner, and the impact on their LTR)? That answer should clue you in to your morals, and I suppose that’s why you posted a thread about it, so you could wrestle with this openly.
I don’t judge people when it comes to sex, love, and relationships. The decisions they make are perfectly valid in their own minds, and my personal views on such things shouldn’t concern them. Only you know what’s right for you; this other person will know what’s right for them.
You should read ArrMatey!'s thread on the same conundrum, written in not-so-gender-neutral tones.