Is my bf and his cousin too close

So my bf has this female cousin he’s really close with. I’ve just started thinking that they are a bit too close like for an example he made a couple like couple videos with her on TikTok and one girl in the comments said if ”everything goes wrong and u don’t find somebody u can marry your cousin” and she just responded with hahahahah I think is a bit weird and they like hug each other a bit too much, his sister told me that they leave her out and they just hang out together.There was this one time they sat in a corner of the couch with a blanket over them and his mom said ”you two are too close” and like when I’m hanging out with them they mostly talk to each other I always feel left out and once she pooped herself and he touched her poop touched like over her pants and it’s a bit too weird for me like should I talk to him about it or am I just overthinking?????????