I think he is not gay but since her brother is kind of girly and was persuing him really hard... He decides to give It a try assuming he would top her brother. "If it's only once it shouldnt be a problem" But than the Brother tried to top him so probably he ran away and that's why the Brother was crying to her
He himself said he was a gay In the chapter. So when he know that she was a girl he okay with it and didnt say he was a bi. i guess when a gay start to like a girl little by little it will end up being a bi. But i think he was becoming a normal lover with her..
demn its look like his ex had come....im still waiting for nxt chapter to know what will happen nxt hahah~
hahaha he's not gay, I think he is bi or maybe its because FL looks like a boy.
PS Thanks uploader-san