Oh, the weirdest of weird. Most girls have fantasies that their boyfriends will never cheat on them, and will just ask for their hand in marriage during an elaborate flash-mob proposal on their birthday. But, there's two reasons, as far as I can ascertain, why that would be arousing to you. First, your sex life is meh. He's not really into it, and yeah he'll fuck you, because you have a penis or vagina or some fun combination of the two, but it's not the toe-curling, electric sex you maybe once had. Or ever had. Maybe you're bad in bed. Maybe you're not confident enough to let yourself go sexually. Whatever's going on, maybe he's not getting all he could get, and you know that. But it's hot to think about him in the throes of passion. It's hot to think about people you're attracted to submit to pleasure. Maybe, the reason why him cheating on you turns you on is that it identifies him as a sexual being, and allows you to envision him how you want him to be with you, which is probably lustful and dirty and seductive. I mean, holy shit, thinking about him as a sexual deviant of some sort is a million times more entertaining than thinking about him as that one nice guy who makes you feel safe. Basically, your him-cheating-on-you fantasy makes him more of an irresistible sex machine than just your garden variety boyfriend. And that's hot hot hot. Know what I mean? Okay, the other reason is this: there is something deep down in your brain, a remnant of evolution if you will, that tells you that a man who can attract and seduce more mates is more fertile and has a better chance of knocking you up. Which is what you want if you're 50,000 year old, pre-hominid you, that that part of your brain still controls your unconscious drives today. So, maybe there's a little part of your brain that thinks him "cheating" on your shows his sexual fertility. But what's pretty important to note, is that fantasies are fantasies for the very reason that if they happened in real life, shit would get so weird. But, if you find yourself hoping and praying that your boyfriend really cheats on you in real life, as opposed to in your mental fantasy world, then to answer your question, yeah, you're a fucking rare gem. I applaud your openness, but you're a rare gem, you are.