What do mean by cheating?
Uke was forced to sleep with the other ml against his will many times and seme got to know that uke is keeping things from him, so he's upset abt it and there's someone who likes him, so he slept with him(as far as i remember).
So both of them cheated on each other?
They slept with other people when they were together, uke always seemed like he didn't like it(and he was being blackmailed to sleep with the other ml) but at same time like he was into it cuz he is drawn like a bitch( and it was always the other ml after him, as far as i remember), but its the seme that went after someone else(i would say that just the seme cheated, but i couldn't say uke didn't do anything, cuz of how he is drawn).
Spoiler
Bad ending, and some cheathing(like it felt like cheating but at same time no for me)