Agree with this comment.
Preach. Yassss.
I would agree but there are some problems with the theory. Maybe it's just poor writing who knows. But it was literally shown our MC didn't feel any even the smallest regret, remorse when he was cheating on his partner. He broke up with him on street and rubbed his infidelity right in said partner's face. He did that in seconds. He didn't even apologise.
He didn't feel regret? The whole chapter 21 is literally about his doubt and kind of regret.
But I know where you're coming from. The MC is an egoistic jerk. He only thinks about himself and what he wants at the moment, he's unable to plan in a long-term perspective (thus his constant failure at work) and just didn't take into consideration that that one moment of bliss he felt with his hyung wasn't worth fucking up his entire life he'd built up.
I keep thinking that Minhyuk hyung was just his unfulfilled fantasy, something he kept dreaming about... But his heart belongs to Seok-Il. At first I was mad at him, but now I truly sympathise with him. He really just mistook fantasy and sexual desire for love. How piteous.