I have only cheated on a romantic partner once in my life, and that was when I was 19 years old (I'm now 50). Since that time, I was always faithful in all my relationships, but I was the "other woman" in affairs where the guy I was seeing was cheating. I do not and will not knowingly participate in that kind of situation anymore, and now find it much more thrilling and exciting to be open and honest about everything.
I do think that cheating on a partner can have a thrill that is similar to the one you can experience by "sleeping with the boss," which I have also done several times. It's exciting to have a secret, to be the only two people in a crowd that know what's going on. The secrecy and sneaking around, pretending that there's no interest or even a passing relationship going on, inside jokes that no one else gets, a look or glance in the middle of an important meeting, the feeling of getting away with something forbidden -- all these elements add to the turn-on. What occurs to me as I write this is that it's almost like role-playing; you have two personas you're trying to live as and manage.
The fact that cheating is more accepted, though, makes it seem more okay to the general public than being out there with poly or open relationships. Even swinging seems to be more accepted than polyamory, perhaps because the image is that it is confined in some way, like a secret. While society seems to be transitioning from that mindset to a more accepting one, hopefully people can see how thrilling and what a turn-on it can be -- since it is currently so different from the "norm," or what's expected -- to have multiple loving relationships in the open, without hiding, and to be truthful about them.