beta
I'm gonna hold your hand when I say this: Cheating is a personality problem. Not everyone is capable of cheating. Even if someone goes through ABSOLUTE HELL (poverty, debt, hunger), if that person has MORALS, they won't even THINK of cheating on their partner. NO MATTER WHAT. They will just break up and end things, because that's the correct and normal thing to do. So the fact that Mincheol was able to cheat on Haesoo, means his morals were bad from the start.
He said during his internal monologue that Haesoo was a challenge to win over, while Ari was not, and he found that a bit boring. Playboys love the attention and sexual pleasure they get from "easy" women, but at the end of the day it bores them and so they look for new women to catch. The author hasn't revealed everything about what went wrong between Mincheol and Haesoo yet, but I can confidently say that Mincheol does not deserve a second chance.