"[He] can lean either way"
I don't think that's what he meant by "I can lean both ways." In this manga the characters act more like real-life gay men than in most yaoi manga, like they don't lose their minds about a man being attracted to another man, the uke doesn't have to be bullied into every little bit of physical affection, etc. so when that senpai said he can go both ways, I'm pretty sure he meant that he switches between top and bottom like most gay men in real life.
That's what I meant
Didn't they not know he was attracted to guys tho?
Senpai is either a power bottom or a top
I think he's the top--calling it now