Where do you get cheating from?? You're mistaken. Shii hasn't slept with Takumi or anyone else since he started "going out" with Tamaki. He's never cheated. He met up with Takumi, but they just talked - understandable since Takumi is the only one Shii has ever been able to discuss his sexuality with - and he refused Takumi's invitation to have sex. He did not "fuck another guy" while being with Tamaki (in whatever tenuous way they are together).
He has no obligation to tell Tamaki that he has had a past sexual relationship, by the way. Especially since Tamaki is likely to be horribly judgemental about it, which Shii is fully aware of. A current partner doesn't owe you their past.
I also agree with sofi, he wasn’t cheating because they weren’t dating at the time. You probably expect someone to have no experience with sex and just assume it might be their first. But you have to be realist sometimes and I think this manga does just that.
Yeah it’s not technically cheating since they weren’t together but I’m still mad that he fucked someone else
And that’s my personal opinion
It's not "not technically cheating", it's not cheating at all.
ok i'm sorry i really thought the seme was going to wait for his friend who was traumatized to come around, but, he decided to fuck another guy. If he couldn't wait for his friend to come around then he should have gone his own way. I hate this guy who will not tell his friend he was fucking someone else. now what....his friend is really trying to be with him, and he got away with his cheating??? such an asshole.