Boyfriends cousin 🙄

My boyfriends cousin recently came in to his life and his families a couple months ago, and she's down in town visiting them. well whenever she first saw my boyfriend her instant reaction was "he's really cute" (LIKE WHAT COUSIN SAYS THAT) I know I'm being stupid making a big deal about a cousin, but it's just irritating! a couple days ago my boyfriend called his mom but his cousin answered and refused to pass the phone to his mom, saying how they haven't talked in a while and she had been thinking about him the whole day (AGAIN WHAT COUSIN SAYS THIS) he told me not to tell her anything about it and just forget it, but how can I? It's not a I'm worried he's gonna leave me for his cousin like seriously lol, but should she be put in her place?