My best friend is being weird and idk what to do?

Here’s a little back story. Me and this girl were buds way back when and kinda lost contact through our school years, then when I moved to the same university she attends we became best friends. Well she’s been hanging out ALOT with this other girl recently that she was friends with in high school. The girl is a year below us so she barely graduated this year. Anyway, I’ve been asking to hang out with my best friend for a few days now and it seems like she always has an excuse. But yet I check her bitmoji on Snapchat or else I see her story and she’s always at the grocery store that this other girl works at or else she’s at this girls house. I mean yeah I understand that she was her friend before I was and they have a lot in common considering they were both on the flag team in hs, but I feel a little bit left out right about now and idk what to do. I don’t wanna be that petty bitch that says this girl is trying to steal my friend away from me but that’s literally what it feels like and I’m at a loss. Yes I’m 19 and I shouldn’t even worry about it that much but what the hell you know?