Ladies, were you ever bothered by your boyfriend's or husband's past?

I'm really bothered by my boyfriend's past even though it's nothing. I'm pretty sure it's because of my OCD that I keep obsessing over it but I'd still like to stop it somehow. Basically, he went out with a girl who was his best friend and they lasted for two weeks. She dumped him and they're not friends at all anymore. He ured me that she ended up fake and he dislikes her now. But the fact that they went out still bothers me. I'm always comparing myself to her even though he's said I'm better and I can honestly say I have a lot more going for me. Why could this be? How do I stop it? We've been going out for 7 months now and he told me he loved me first and brought up marriage. Despite that, I always start arguments because I'm still paranoid. When I start them, he always insists that I just forget the past because he wants to focus on us. But I just can't. x[. Are any of you the same way with your boyfriends and husbands? How are you getting over it or how did you get over it?