Help me find this YA romance book about a love triangle with a high school guy who is the “beard” for his close girl friend (read around 2016-2018)

Hi everyone! I’m trying to remember the title of a YA romance I read in high school (probably between 2016-2018). Here’s what I recall:

The story starts with the main character (a girl) and her best friend at a pool. Later, the main girl sees her best friend kissing her boyfriend and gets really freaked out—she even throws up. Then a new guy comes to help her, and the story focuses on their developing romance. Complication: the new guy seems to have a girlfriend, but it turns out she’s a closeted lesbian who uses him as a “beard” (fake boyfriend) because she hasn’t come out yet. The book is not an LGBTQ romance—the main love story is between the girl and the new guy. Does this sound familiar to anyone? Any guesses or suggestions would be so appreciated!

Thanks in advance!