I'm in the same position love but my dad doesn't yell at me he just ignores me most of the time but yeah tell him what sweet-tart said.Although I told my dad and he just ignores it but try it!
i'm with sweet-tart on this one. but to give a little clearer advice, i would stay away from trying to put the blame on your step-mum, because that's just going to make him defensive, most likely. just tell him what HE'S doing and how THOSE things make you feel. keep it as simple and heartfelt as possible. i hate it when i feel like i can't confide the important things in my life to my family, and it kinda seems like that's how you feel right now. i sorry. =[
Just tell him how you feel. Not all good things come to an end, he's your dad and he's going to be there for you always. Me and my dad had a falling out a couple years ago but now we're just as tight as ever because I told him. If he really loves you then he'll listen and understand. Trust me. :D