My guy friend ( of around 8 years we wrestled on the same team gr 6-12,he was the team captain of the high school wrestling team I wrestled on, now he’s a university wrestler and I’m a female middle school wrestling coach) has a girlfriend he’s been dating for around 4 years. I think of her as also being my friend and she’s always been friendly towards me but when I see her with him its like she’s a good friend of mine and I enjoy hanging out with both of them but when he’s not around it’s like she’s a friend of a friend.
So lately it’s seemed like she isn’t actually my friend but is just nice to me because I’m friends with her boyfriend. Which is annoying because I don’t have very many girlfriends ( I am a bit shy and she’s really outgoing) and I think of her boyfriend as a good friend ( and like an older brother to me,even though he’s the same age as me). Also after high school most of my friends moved away ( and he’s away at university, home during holidays, some weekends, and summer) but her and I both still live in our small hometown so we see each other often. ( the 3 of us are age 20, turning 21 this year).
So do you think we are friends, how do I become better friends with her, is she jealous of my friendship with her boyfriend?

I think you are just acquaintances because of your guy friend. Best buddies? Hardly and after all this time it's probably as good as it's going to get, until you are ready to shed some shyness and explore being better friends, without your guy friend. If all you have in common is your friend, then you haven't gotten past acquaintances.

Your shy around other girls? Hard to make new friends that way. Engage her beyond your guy friend and find out if you can be friends. Friends is a two way street you know. You can't expect others to always put forth the effort can you?