What? Middle school ages are different in Japan. Hayato was like 15 and the other guy was like 16-17. Plus, we don't know when they started dating and when they were found out. Stop trying to justify what Hayato did just because he was a kid. Both of them were teenagers at the time. He wasn't "groomed", Hayato consented to it and loved the guy.
All of you people are full of bullshit lol we don't know their age gap to say Hayato was groomed or whatever, they could be a year apart. They probably went to different high schools and that's how they were able to get away with their affair. Hayato's big brother being the genius kid that he is was possibly always busy with student council or something.
In volume 1 hayato said that the guy told him that his brother didn't love him anymore and instead loved Hayato, and honestly he was just kind of a delusional middle schooler with only love on his brain, plus the fact that he was struggling with coming to terms with his sexuality and probably felt like the time he spent with Urabe's older brother was kind of an escape. He probably thought what he was doing was justified since they "loved" each other and that what Urabe's bro had going on with his bro wasn't serious anymore. I would actually place more of a blame on Urabe's brother since he is older and it's wrong of him to be leading on a more influential younger person. He shouldn't have approached him or given him any false hope period. And I'm not justifying Hayato's actions here since he was involved and probably had some guilty conscience since the guy was dating his brother. I am just giving reasons for why he followed through and sympathizing with his situation.
It's annoying that people are going so easy on him and placing all the blame onto the cheater. Hayato was old enough to understand that what he and that guy was doing was terrible and they were both teenagers, it was like a 2 or 3 yr age gap. They are both shitty people for what they did, stay mad lol. We don't know when they started dating, when they were found out, or their age gap stfu. Both of them were kids, stop babying Hayato he know what he was doing was wrong but didn't care.