figuring out my issues

I never understood why i have so much issues with my father. Its a really touchy nerve that i rarely like to mention. Now im not saying there aren't things from my mother i don't resent. Lets be honest we all resent our parents for something. But there are certain things that after you get older you realize you shouldn't resent them for. Theres always that one party that you want to go to that you're not allowed, or that get together that you couldnt get to because you had to be with your parents. Maybe they dont understand today what we want to have in our future or what we think is right for us. As we grow up we make choices of our own, but while we're still with our parents they give their opinions and more times than not disagree with our choices.
But my Father who i usually call my sperm donor. Most of the time i feel like he really hasnt been ther for me. He is just my biological father not my dad who helped me make choices in life and taught me lessons. Its not that he doesnt try to teach me things, but it feels like he does too little too late. He tries to give me lessons that i dont need or have already been taught by my mother. He also seems to fail to realize that i know more than what he thinks i know and actually understand it.  somedays i feel like if he still thinks im as old as when he left. I was 8 years old, & what he fails to realize is that i understand that he didn;t leave exactly by choice it was more because my mother kicked him out. But like two people can have their differences so did they. It was something that on days i wish i couldnt remember. There are events that even though to someone else they may not have been traumatizing, to me i think they were. They're things that i find that i will think about it for no reason at all. A memory of what has happened over time. Or just a second of a realization.
My memories take me back to arguments, or my father thinking i shouldnt understand things that were going on. I've always known too much for my own good. Something that i feel my father fails to realize. Somedays i feel like he doesnt value my choices or my thought process. but theres not much i can doo because i feel that when i try to express myself he doesnt listen.
Yet i can never figure out my exact issue with him. Its like i could say i forgive him but if he does or say something, i use everything that has ever happened to take it out on him. I go back to being upset about every little thing he has done wrong in my life. But i shouldnt because we should leave the past behind us, but it becomes so hard that it inexplicable

& even though i have written all this i cant seem to be able to point one thing out. Am i mad because he left? am i mad beacuse he cheated? am i mad because he hasnt been there when i needed. am i mad because he treats me like im stupid? am i mad because i think he makes the wrong choices? am i mad because he doesnt think before he speaks? am i mad because he would disappear without any explination? i dont know why im mad, but i just am. its a grudge that i cant seem to get over. and no matter how much i try to get over it i cant figure out how to get over it.