What should I do about my problems with my dad? Please help!?

I am a teen. My parents got a divorce when I was a toddler. I lived with my mom and visited my dad. But shortly my dad just quit getting in contact with us. When he did phone us he lied constitly. When got married five years ago, to the woman he cheated on my mom with, I was asked to be in his wedding and I though it was a turning point but it wasn't. Now I only see him on my bday, my bros bday, xmas and when he has parties at his house. I think he does it make himself look good. I sent him a letter two months ago telling my feelngs and he never responded. My bday is coming up and I'm gonna feel weird. Last year since my bday was on fathers day the supper he takes me to for my bdy present he took my stepmom's father along for his fathers day present. And to make it worse I didn't even get to chose the place her dad did. What should I do? I really want to work things out but I don't know how or why it is like this? Is he embarrested by us? Please help!