Am I over thinking this?!

So my boyfriend and I have been together 6 months and he told me when we first starting dating about a girl he "dated" who ended up being his cousin by marriage and when they found out they broke up. Well I guess they still talk which I was okay with cause it's his cousin but for some reason she has me blocked on fb. I only found this out because he posted posted a status and someone commented on it and I couldn't see who it was so a friend of mine went and looked and sent me a screenshot and it was this cousin. Well now I'm kinda worried like what of she really isn't a cousin and he's lying. She moves far away from us and I have it in my head that maybe he's just with me because she doesn't live in our area anymore. I want to ask him why I am blocked from her page but I don't want to bring it up and say why I'm worried and look like an idiot and it start a fight. Idk what to do I need some serious advice!