Feel weird around him.....?

[bubba]

Ok my girlfriends best friend she's known for like her whole life is always wanting to hang out with us when were not really doin anything he's cool and everything I just become a different person around him I get all quiet dnt really talk that much Cus their always talking having their own little stories and shit and idk it's like she doesn't really talk to me when he's around so what can I do to become better friends with him and be able to talk with them instead of just sitting there like a dumbass haha ya so please help me out