Need a second opinion 🆘

So I’m dating this boy or whatever, me my cousin & my sister all met him, his friends at the mall we are all friends BUT... every time we talk about certain situations (me & my boyfriend) he always brings up my cousin like for example if I say something that would happen he says “I bet so & so would do this” you know ? Like they don’t text or anything but it’s just weird like some things we talk about it’s no reason to bring her up idk .. I mean I’ve had history with my cousin talking to people I have liked in the past but I know for sure they aren’t talking but it’s just weird like I never had that happen . Like if he likes her that’s cool but he’s not about to like her & mess with me. What should I do ?! I don’t wanna sound awkward with it like how would I bring it up ?! I have even talked to my sister about it, she thinks it’s weird also.