First of all, I think this season got an unfair bad rep.
I love flawed characters so I enjoyed every minute of it. Cheating is bad but it's also something that happens in real life, I personally think people are more upset that it was "perfect" Korn that cheated, instead of Knock.
Korn and Knock both had their flaws. Knock was childish, self absorbed and took Korn for granted but he also had a legitimate reason to be upset with Korn about hiding him. Knock basically turned his life upside down to be with Korn and now he's partly in the closet because of him.
Korn was basically the adult in the relationship, while also stressed out about his father's homophobia. It's unfortunate that he fell for Pete's scheme but sometimes good people mess up.
Communication has always been an issue with them so I wasn't surprised to see it happen again, yes people should grow but fixing bad communication takes time in real life. I'm happy the show was brave enough to tackle cheating and I'm ok with the way it was handled. Korn and Knock were devastated, but in the end their relationship was the better for it. They both realized that they loved each other regardless of everything happening and Knock especially got feedback from friends and could see how he took Korn for granted.
I'm not much for heterosexual ships, so I can't comment on Yiwha and Cho. I'm also going to ignore the Farm and Bright relationship.
Overall a beautiful end to a wonderful story