Seeing friends having interactions makes me feel bad

I talk with 2 big friends of mine everyday, and well i love them a lot, but anytime they are playful towards each other, crack a joke i dont understand, say a reference i dont understand, or just laugh to each other i feel so angry and sad it makes me question if i really am a good friend to them or not. It's a visceral stomach pain i feel every time they do it, and its not like they dont interact with me or laugh with me, i at least think they like me but i can never be sure cuz im always doubting it. It's honestly exausting and im considering leaving them, because i think they would be better off without me.