How do I come out of sexual harassment of my step mom?

I'm 14 yr old boy. My mom has expired 5 yrs ago and dad brought in a step mom a couple of years ago. She and I couldn't get along each other and I hated her too. She was in no way similar to my mom and younger to mom also.. But recently she started behaving more sexually with me.
she intentionally touches me..sleeps along with me when my
dad is usually out of station on business
she is very skinny and and tries to make me feel attracted towards her
i feel guilty and unethical of what i'm involved in..but when she seduces me i cant control.