He should've been honest with him yes. BUT honey, it's not easy. Hello? He was raped and he doesn't know he was. He believes it was his fault they had sex and so he thinks he cheated on his boyfriend. Damn it isn't easy at all. To him this is confessing his mistake. He needs time. Jeez, if we already know the whole story and we are kinda getting angry at him for not saying anything still, no wonder he's fucking scared to tell him, considering he knows nothing.
From what I saw in the raws things are getting bad and then better.
Yes, it's so easy to resolve anything with communication but this manga deals it more realistically cause irl there are actually countless rape victims that never say anything in fear of not being taken seriously or think they'll be downgraded as a slut. Dont compare It to other yaoi with the miscommunication that is stupid jealousy tropes, etc.
Don't get me wrong, Youngmin-hyung was the victim. His professor raped him - that is not Youngmin's fault. But he should have been honest with Jungwoo the moment it happened, instead of concealing it and, in the process, lying to him. I don't know how many times a yaoi/shounen ai manga has made me scream "JUST COMMUNICATE ALREADY!!" at the top of my lungs, but I do know that this one has had me screaming it every chapter. Be HONEST with Jungwoo, Youngmin. Tell him what happened. Things will only keep getting worse (both socially and psychologically) if you keep hiding the truth from your loved one.