It's fine that you break up because you realized you were gay, but you can't just write away the hurt she'll feel. Apologize, accept that you hurt someone, and make amends. Seriously.
What a freaking jerk...
Sure it might hurt her to find out that he's gay but the way he "explained" it was so "douchey" like he wants her to understand and accept it right away with a smile like it's nothing and said that a nice person would do just that...is he a nice person himself???!!!....NO!!!
Hope that gay dude lives his whole life ALONE & MISERABLE...
Dude, her ex is a total douchebag. You don't just use people to figure out your sexual orientation. Just because you're gay doesn't mean you can use people and get away with it without even apologizing.