I think it was the biggest problem when they were young but Cheol kind of accepts it better as an adult. The biggest problem now seems to be that Minyoung inflicted him a major emotional and psychological blow and just went offline after that. Which Cheol interpreted as Minyoung only playing with his feelings all along. So, chattered trust. An even now Minyoung has expressed very clearly that he wants to come back together, but he still expressed no regret and is yet to explain why he didn't make contact after the incident. Can't blame Cheol for feeling distrustfull and insecure...
I agree with what the other person said. But I'd like to add that it seems that Cheol would have forgiven Minyoung back when they were young if only Minyoung had come back. Cheol has never had someone who 100% supported him. Even his uncle, who seems to love him a lot, didn't want to admit that something was wrong in Cheol's house. He was in denial because he loved his brother and didn't want to admit that his brother was a bad father to Cheol.
But Minyoung loved Cheol unconditionally. And then he betrayed him by outing him and leaving without saying goodbye. Cheol, as an adult, seems better at standing up for himself. However, I don't think he'll forgive Minyoung unless Minyoung apologizes for what he did and explains his actions. I really do wonder why he did what he did.
Actually it's none of that. When he was young the reason he finds it hard to love Minyoung is because he "hates" him. He "hated" Minyoung for being so blessed. He "hated" Minyoung for always taking the 1st place in the exams which Jeong is constantly berated by his father for not getting.
In his adult life, he finds it hard to love Minyoung again because he felt deeply betrayed and abandoned by Minyoung. Jeong had no one in his life. His own family is abusive af and he doesn't even have a friend. Minyoung was the only one who was ever there for him. But for some reasons we still didn't know, Minyoung outed Jeong to his abusive father and disappeared for years, leaving Jeong all alone again and under the abuse of his father that hated he was gay. That's why Jeong got pressured in to get married to a woman. And that's why he haaaated Minyoung so much.

I feel like Cheol has so much internalized homophobia bc of his dad and that’s why he finds it so hard to accept that he still does love minyoung. But likeeeee factoring in the fact minyoung is crazy asf I wouldn’t love him either