Spoilers
I don't remember exactly which chapter of the novel it happens in since I'm reading this for a while now, but he does find out. It takes some time, though.
They have a lot of R19 scenes first (with both of Haryang's identities), start dating, Yegyeol eventually learns about his senior brother's secrets.... A lot of things happens hahahha
He only finds out after Yegyeol gets trapped in an hallucination of the day those Espers killed his parents. He almost ends up killing Haryang with his Esper powers while he's under the illusion. After he breaks free, he tells Haryang everything with a lot of fear of being abandoned, but senior brother believes it in him and says he will never abandon him. Then, Haryang starts teaching him martial arts so he can use his Esper powers more effectively in combat without anyone realizing that he has this strange power and "Senior brother" became "Master" instead hahahha

Does the Senior ever learn that Yegyeol did indeed die before and died again the future before he was brought back? If so, can I get the novel ch? thanks in advance