Why does my mom do this?

I love my mother and I really would never want to do anything dis respectful. But she is really bothering my gf and me. I moved out of her house because she was very controling (me and my gf are both 22) anyways she came banging on my door today because she found out I had a gf and was like “no girls allowed” I told her to leave. She did not listen, my gf called the police.

My mom told the police that “hes my son, hes not allowed to have girls over.” I did not press charges on her. But I really wish I knew how to handle this. Me and my gf work together and always will.