Boyfriend hanging out with questionable ex?

Alright so I'm an extremely laid back girlfriend. At least compared to the people I know. I never question him and feel totally fine with him hanging out with girls and going out without me. I've never invaded his privacy or gone out of my way to snoop. I hardly have ANY jealousy at ALL. But lately his ex girlfriend has been around quite a bit. She's from a different town and they only dated for four months. Me and him have now been dating for 5. It's nothing super serious though. He claims that HE broke up with her when she moved despite her saying she would stay for him. This was last summer and ive heard her mentioned quite a bit. "Sammie this Sammie that" always talking about how "dumb" and "immature" she was which I think is strange because he never talks that way about any other relationships. Now i see her name every day in my Facebook notifications. She comments on every single thing I comment on. Posts on his wall talking about how much she likes his pictures. She constantly has status's about "wanting a boy with a nose ring and dyed hair" something my boyfriend has both of. I admit I have stalked her on Facebook a bit I couldn't help myself I was curious about this infamous girl. Apparently he went clubbing with her a week before we were officially dating but still a "thing" the other night we were taking separate cars to the same party. When he was 20 minutes late I texted him asking where he was and apparently Sammie had called him saying she still loved him. He has never said anything to her about no longer being interested. And I'm not the type to worry but I'm finding myself freaked out and jealous. Something I'm not used to. Should I be worried? Or am I just being paranoid? Sorry this was so long I just really need some help :(