Well my boyfriend and I used to be tight and everything but lately it seems I can't do anything right....it all started out when my ex came back and told me to choose between him or my boyfriend and so I picked my boyfriend and when I told him he started acting mean and saying rude stuff. He said there wasn't anything wrong but I don't believe him I have tried everything he cays he loves me but he's been treating all of the people he said he didn't even like better that me...Why is he doing this?
He's possibly pissed at your ex.....but your ex isn't around him, so he's angry with no one to take it out on except you. I could be wrong, but I think you should tell him how you feel and ask him why he's doing this. It might be that it's just going to take some time for him to work out his anger. However, if he gets abusive- leave. Don't question it, think about it or hope.....leave.
It's hard to say why he may be doing something like this. I can sit here and list off to you a couple different thoughts, but that's all they would be, thoughts.
One thing you did not mention was if you had spoken to him about this or not. If you have not I would do so and tell him what you have told us here and then update us on how the conversation went. If you have already talked to him about it then Let us know what happened.