help idk what to do

I’ve been dating this guy for awhile now but it’s a long distance relationship, everything was good fine until a couple weeks ago he just sent a snap of this random girl I’ve never seen before and I asked who she was and he said she’s one of his good friends and he should’ve told me sooner and I thought that was the end of it but now we hardly talk and on Halloween he posted them carving pumpkins(he’s never posted me) and again today he sent snaps of her. I’ve been telling myself that it’s probably nothing and it’s just my trust issues but at same time I can’t help but feel like he’s cheating idk if I should stay with him or just leave