Im a step parent....need advice?

im a step mom to a 12 almost 13 year old boy. he totaly hates me, and im not joking. his dad and i have been married for 7 years, and he still doesnt like me. we let him live with us for three months last year, and he started goin to the school telling lies on ME not his dad and i thought they were goin to get dss involved until they found out he was lying. i dont know what else to do. does he hate me that much, or could his mom have something to do with it? shes tried to get my husband back for years now. any advice???