To be honest with you when you have a disorder like OCD, it really does require treatment. It doesn't just go away on its own. Here is a link to a very good article about OCD. To say your "family doesn't really go to doctor's" isn't going to help you very much.
http://www.wsps.info/index.php?catid=0:&id=82:ten-things-you-need-to-know-to-overcome-ocd&option=com_content&view=article
No my family doesn't really go to doctor's but we have friends that are and everyone I've talked to says I have it. And no I haven't been treated for it.
Have you been formally diagnosed with OCD? If you have, have you ever had treatment for it?
She's never done anything to bother me she's kinda the only friend I have and I've gotten used to the thought of her being with my brother but these thoughts have gotten to the point where whenever I'm around her I can't stop questioning if I enjoy being around her to the point where I Don't because I can't get that question in my mind to stop. I want to enjoy being around her because soon she's gonna be family so it would be great to be best friends with my sister in law. I guess I'm fearful being I broke up with my boyfriend because I couldn't get my ocd in control and I'm terrified that's gonna happen with her because she's the only friend I've got. Is there anyway to stop obsessing over this and just be friends with her?
Is there something she did that you are bothered by? You describe her as a good friend. Everybody gets in a bad mood and when they are that way they usually just want to be by themselves. Maybe her presence was what annoyed you because you wanted to be alone. That is not her fault. She is not a mind reader. Remember, it doesn't sound like something she did but rather you yourself who wanted to be by yourself. What are you afraid of? It sounds like you may be fearful of losing her friendship now.