"we were practically inseperable, seeing each other every day nearly. Then he needed some space a couple of nights a week and I found out he had been talking to his friend about it. She's a girl who I hate, hence why i'm even more paranoid that he's cheating on me with her. Deep down I don't think he would though, he's such a good guy. I know he loves me. It's just me and my head."
I was exactly the same as this and it near enough ruined my relationship.
You've just gotta let it go and ignore it, find something else to focus your mind on, the more time he spends with this girl the more i trust him. I know it sounds crazy but it's true. it's hard i know that but it can be done.
Good luck x