There was a boy, that I like it.. He had a "girlfriend" who was with him in his the most depressing moments so he wasn't prepared to broke up with her soon, and we made a deal to pretend that we are just friends.But when she find out that we already been together she broke up with him I think. Then I tried to talk to him first in social sites, but he never returned to my messages.
I need an advice what to do?
Should I pretend that nothing happened or what?

Ps:Sorry if there is mistakes, my English is not very good :)

He had a girlfriend. Instead of doing the decent thing and breaking up with her so he could be with you, he cheated on the girlfriend.

This sounds very much like a case of regret. He stayed with the girlfriend for a reason, and not because she's been there for him when he's been depressed. He stayed with her because he wanted to be with her. He cheated with you because you were willing. Now he's lost the person he actually cared about, and instead of blaming himself, he blames you. He doesn't see that it's his own actions that cost him the person he actually wants to be with. He thinks it's your fault.

Bottom line, he doesn't want to be with you. He never did. You were a distraction, excitement, but that's it. If he had wanted to be with you, he would have dumped the girlfriend. The girlfriend is who matters to him. You don't. Sorry, but the truth is often harsh.

Forget about him and move on, hopefully to someone that isn't in a relationship.

So... you tried to steal him from another girl, but in the end another girl stole him from you.

We call that karma... what goes around comes around.

Stealing, lying, cheating, and pretending, and deceiving didn't work. Never does. Hope you learned something that will help you know to do the right thing, the right way, next time.