Oh this is a great one, gives us insight into peoples' motivation to do (or not do) something...Very constructive - would make a great question for new couples to ask each other...
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So back to the question ... What keeps me from cheating???..
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I'd have to say .....His Shoes...I put myself in his shoes all the time, try to see things from his perspective, if you will...It's how I guage whether I've crossed my and/or his lines, acted inappropriately for someone in an exclusive relationship and determine if it's something I'll regret later...
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It's 2nd nature to me & takes but a nano second to run the battery test ... with questions like ... "If he walked in right now, to see and hear this, would, what I'm doing hurt him?".."If I knew he was doing what I'm doing, would it hurt me?"..
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Altho the fear & my own feeling options u gave may come into play I think the real reason is I feel I'm protector of my SO's ego & partially responsible for his emotional well-being & I take that seriously...

I'm just monogamous by nature and I wouldn't want to hurt him, it's never been a temptation...

Choice D, all of the above. I can't separate out my own feeling that cheating is wrong from society's message that cheating is wrong; they're too closely intertwined. And the repercussions would stem from both of those in turn. Being afraid of being caught means that I'd be afraid of what others would think of me, and what my partner would feel and do in response. So, it's all those things, plus the fact that I'm mostly satisfied with Mr. O and have no need to seek satisfaction elsewhere. Also, who's got the time? If I had any spare time in which to have an affair, I'd use it to nap instead...

Passion. Passion for my partner...
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-Carlos..
Angie's my passion...

I love my partner and respect him so much, I have no desire whatsoever to cheat. Not even tempted...