Step-Mother Blackmailing Me.?

I'm 17, My stepmother is 29 and my father is 41. 2 years ago my father remarried and I got a new stepmom, I was 15 and she was 27, after 6 months of marriage, she forced me to have with her, I was shocked and a virgin and I didn't know what to do, I didn't tell my father of course cuz he seemed happy about the marriage thing...after that it got worse, she would force me to have with her everyday and we do it countless times each day...it went along for 2 years...I can't tell my father because she is blackmailing me about telling him that I forced her and such and I will get kicked out of the house etc...I want to get out of this situation...she ruins my relationships with other girls and I have to do what she tells me always...I can't even stay out late..I have to get home back by midnight or else she will "punish" me...She's young, attractive and manipulative...I want to get out of this badly....any suggestions please?