I'm being used for a greencard?

Help me please! I want to get out of this situation. I married a Mexican man who I now realize only wanted me for a greencard. In the beginning he and his family were very welcoming and accepting Now its an entirely different story. His behavior has changed. He went from being a quiet, shy and attentive person to this arrogant aggressive self serving prick. Now he's telling me that he wants to stay married but that he wants to be free to date. What nerve!!! I don't trust him or his mom. He's a liar, a cheat, and a very manipulative cunning man. What's going to happen? I feel hurt, deceived, taken advantage of, and guilted. They've made it my responsibility to give him the American the dream. My insides are screaming NO! , get a divorce and run as fast as you can. Its painful to realize that someone you looked at with love never looked at you the same. I don't matter to these people. I'm a stepping stone to the American dream. It doesn't matter who they step on emotionally to get the