reread it too... shit it could be really hard for me too if it turns out it was him noooo DX
But that guy said, he didn't have a lover for a while! So probably not
I don't think he is... The big bro probably has a girlfriend (stereotypically (I don't even know if that's a real word) it should be the club manager ^^) and that "mom"guy is the sempai I think
He is a sensei, but I don't think he is the lover. He even mentioned how he is single and is interested in Kou.
Plus he got Kou's name so I think he knows whose brother he is.
Shit! I reread again...and now im scared if that mom guy is his brother's lover. If so...its gonna hard for him to accept it