I have been ruining my moms marraige since i was 6..i want it to end.?

Im almost 19 and i never had a dad.My real dad was a skeez and my mom left him when i was an infant.My mom was never around because she was a flight attendent i lived with my grandma.When i was 6 my mom remarried.My step dad has always hated me.He sees me as this huge burden in their marraige,im the bad seed even when i do nothing.Him and my mom are ALWAYS everynight since i was 6 fighting about me.My mom defends me,My step dad argues about what a bad kid i am and how im a pain.My mom and step dad had 2 kids which he loves to death.when i was little he never hugged or kissed me.To this day iv barely gotten a hug much less a kiss.I feel like im ruining my moms life.I dont know if i should leave the house or what i should do,i feel so helpless.I dont want to ruin my moms life.My step dad hates my guts and thats why they always fight.because of me. Please help...i dont know what do .I have always felt like an oddball and alone.I have never had a father...and i love my mom ,i dont wanna ruin her life anymore.