Need advice

need some advice here. girlfriend went on a trip down South with her friends I didn't think anything of it but since she came back shes been distant and not wanting to hangout. asked if they met anyone their age down there or if it was all older people she said they didn't socialize. I also didn't think anything of that until I saw a guy comment on her Instagram who's not from here and his only mutual follower was her. should I bring this up or leave it be? first-time poster thanks