Terrible relashionship with my mother

Hi, i really Need your help because althought i also want to have a good relashionship with my mother, i also spoils my relashionship with my bf. So, I have a Terrible relashionship with my mother because she dont like any one of my friends and dont support the fact that I have a bf. Each time I speak with him she takes me the computer or the phone and she dont let me to be with him (every time we are together is without anyone knowing). She is always Telling that I Am 15 and him 17, that im a Child and that it does not have age for dating. Im fed up of this !!! Someone can help me??