Hi there. I've written this several times but I think whether we are gay or not is based in our genetics. We don't wake up one day and become gay. Who we are attracted to is hardwired in our genetic background. For instance, if I see a good looking man, I don't have to think about it...my body just reacts. Now if I see a good looking woman, my reaction is always one of comparison. Do I look as good or I like her hair or I wish I had a body like hers....that kind of stuff.
OCD is fighting a war with your own brain. You say black and your brain says white. What you need to learn is how to deal with the thoughts when they show up. You have to give them no credit. When you do that, when you take the fear away from the thought, it will go away.
If you stood up right now and said "I'm gay" do you think you would want to run out and get a boyfriend? If the answer is no, then you cannot be gay.
Here is a bit more information about OCD in general and how you can overcome it.