Hi momof5. The first thought that came to me is.. where is this boy's bio mom? By all this ridiculous behavior, and hostility towards you, I'd say he's missing his mother, possibly resents her for not being in his life enough, if at all, and like jkgrandma said, he's taking it out on you!
I'd sit down with him and ask him strait out if he misses his mom, if he's mad at her. Ask him about problems with kids or Teachers at school. Maybe if you show him some compassion and concern rather than your personal frustration and vulnerability, he will see you as remaining the Parent, not an available 'oppertunity' to vent his emotions.
My best advise to you, (as a step-mom myself) would be to stay in control. Nip it in the bud with him now. It sounds like he's lost respect for MOMS.. which could cause him to lose respect for women, forever. Cut this boy off at the pass sister! While there's still time. You are the adult, his role model, you can do this with dignity.