Lots of times taking the piss is only fun for the one taking the piss.
My thoughts are that you made him feel insecure about yours and his relationship, that you were passive aggressively suggesting that you didn't feel like he was in to you or that you don't feel like he's mainly enough or hetero enough for you. Also, even if he's not generally homophobic, having the girl you're sleeping with and having sex with suggest to a guy that she either consciously or unconsciously thinks he's homosexual will feel like an attack on his masculinity because it's clear from that that on some level YOU think there's something wrong with his masculinity or his virility or his ability to satisfy you sexually. Why? Because so, so, so many times the first thing a girl does to a guy who's not interested in her or rebuffs her advances is accuse him of being gay, like being gay is the only conceivable reason a guy wouldn't want her. So, his feeling dejected and insecurity comes from a place where you think there's something lacking in his attraction towards you. That's enough to bum anyone out, especially when you consider how often girls couch what they say with a much deeper meaning.
About a great many things you can take the piss and a guy will roll with it. But not about his penis, not about his sexual performance, and not about his sexuality. You don't hit a guy below the belt.