No you read it right. It's a little confusing but I think it's from what his ex-teammate would have said. That because the ex-teammate and ex-lover wear in a FB situation the ML butting in made him the cheater. Which is silly.
i think its because his lover and teammate were already in this fwb relationship before minjae and his lover got together. i am presuming that the teammate actually had feelings for minjae's lover so when he found out their relationship, he accused minjae for coming between them, making it seem like minjae was the cheater (tho idk why he is referred to as that cuz it shouldve been like a mistress but a man) when it was actually the lover who is the cheater. idk for sure but thats what i understood atleast TT
Also what did Minjae mean by saying he was the cheater? Wasn't it the other way around? Unless I read this wrongly