I told a guy with a girlfriend that I like him. Does that make me a skank?

Alright so long story short, I have been really good friends with a guy for more than a year now. I had a crush on him before he got a girlfriend, but since then I've accepted the fact that we are just friends. Then, out of the blue, he told me how he wasn't happy in his relationship and hinted that he had feelings for another girl. He wouldn't tell me who it was, but I guessed that it was me and I was right, he told me so. So I told him that I liked him too. And now I just don't know what to do. I'm pretty sure he's going to break up with his girlfriend, but I told him I don't want to be the reason they break up. Help! What should I do? And does this make me slutty?