What would make a guy steal money from a girl he 'cared' about?

A guy that i was friends with for awhile and then became my bf stole money from me via credit card...he withdraw cash and tried to hide it from me. I don't understand why he would do that esp when i was so good to him. Were both young (late teens/early 20s) and have known eachother for while. I thought he was a great guy at first and then down the line he started to become very rude and demand to know how much $ i made etc..he was also very need with no job or schooling with little motivation, but i stayed in his corner. I don't understand why he would do such a hurtful thing to me. I really didn't deserve to get played like this and he said he loved me. why??