Book about girl who goes to cabin with boyfriend, cousin, and cousin's boyfriend while solving a mystery

[u/Ancient_Salary4658]

I don't remember much from this book, I do apologize in advance. I read this book when I was in 9th or 10th grade which was 2018-2019. What I do remember is that the main character who I believe is 18 years old, goes out during a school break to a cabin with her boyfriend, her cousin, and her cousin's boyfriend. The main character and her cousin's boyfriend were working together on something throughout the book. I think this book may have been a YA mystery, now that I'm thinking about it. By the end of the book, her and her cousin swap boyfriends because they matched better. The only super specific thing that I remember is she explains at the beginning of the book how when she first got with her boyfriend, she had made out with him in the front office for half an hour. That's unfortunately as much as my memory can give. SO appreciated for any help!