I do have access to a school counselor, but really I think I am just going to start talking to my pastor more and more, he knows my situation without me having to explain it to him. He knows exactly what has happened (known him since I was 5). I am concerned that if I go to a school counselor I might say something wrong in my story or something and completely screw up any advice I could get.
You shouldn't worry about not being able to tell the story blow-by-blow, I'm sure the counsellor is familiar enough with the scenario. As mentioned by others, the counsellor is there to listen - to let you blow of steam. If the counsellor does more talking than listening - go to a different one.
Their job is to listen and pose questions that help you work through your own issue, and offer options and alternatives. They don't actually fix your problem.
I have been a step-parent to 3 great kids for the past 10 years. While there are some similarities with your story our situation was less venomous - to avoid the issues that you are having. Even with us being very civil about things, my eldest step-daughter (8 when her parent seperated) took it the hardest. From time to time over the years she has gone to the school counsellor. And has found it very helpful.
We didn't know that she was going to the counsellor, but when she was about 15 she let slip over dinner one night that she went to the counsellor that day. The look on her face stays with me today. She thought we would be mad at her. We told her it was OK with us and that we loved her very much, and if she ever wanted either of us to come with her we'd be happy to. We also made it clear to the others as well.
You will come out the other end of this situation. Life presents us all with challenges and while it can be terribly hard at the time, these situations allow us to build character and strength.
Believe in yourself, your future and that when you get married and have kids you'll have a perspective that will allow you to parent your own kids with more love and respect.