Need some reassurance ladies...

Ok so my S.O. is having a breakfast date with his best friend tomorrow mornin that he only gets to see once, maybe twice a year... wouldn't be a problem for me except his bestie is a woman... Now she has been in his life a lot longer than I have, but am I insanely jealous for no reason? Or is this normal? I've haven't personally met her, but from the way he talks she is great. I'm not normally a jealous person, I don't mind female friends, never have. But for some reason this feels different. I'm not going to use the "L" word here, but I really like this guy and what we have together. And I've had some pretty crappy relationships in the past, my son's father being the worst. I waited almost 2 years before getting back into a relationship. I mean, is this just part of having a real relationship and being an adult? (I'm 26 and I've only had a couple of adult relationships that were nowhere near this good). Help me out here y'all.