Get the fuck out of there. Call a child abuse help line and ask them for help. Explain the situation to a friend, and ask if you can stay at their house. Your mother's behavior is unacceptable, and you aren't safe with her right now.

Also - you are not a slut. You are a normal (almost) adult female, with normal sexual urges. And you're focusing those urges on a boy who, from the sound of it, is a good thing in your life.