When I was younger I used to always think, 'karma will get them', 'they'll really regret it' 'they'll lose a lot of respect from people' and so on.
Now with age, it's pretty clear that people who cheat usually just get on happily with their lives, most people accept the new couple, don't fall out, the couple often stay happily together, and life goes on as normal for them.
I remember when my ex cheated a few years back. His 2 good mates were pissed off at him for a while and actually supported me over him. Eventually I didn't hear from them again and they ended up becoming close friends with his new girlfriend, the woman he'd cheated with. I expected it really and knew their loyalties had lied with him.
I still think it's disgusting to cheat.