Boyfriends girl-friend😅

Okay so my boyfriend is friends with this girl and they’re both in the same circle of friends, my boyfriend and that girl have done some stuff in the past but when we got together he told me that it was in past, and was just experimenting what can be going on there- but ended up being nothing. It’s just so awkward when we all hangout because I just feel like she still does like him even though she has a boyfriend. Am I wrong? Am I overthinking and just being annoying?? HELP!! Haha