The Love Wager by Lynn Painter

Two people make a wager on who can find love first, not realizing what they should be betting on is each other, in this new romantic comedy by Lynn Painter, New York Times bestselling author of Mr. Wrong Number.
Hallie Piper is turning over a new leaf. After belly-crawling out of a hotel room (hello, rock bottom), she decides it's time to become a full-on adult. She gets a new apartment, a new haircut, and a new wardrobe, but when she logs onto the dating app that she has determined will find her new love, she sees none other than Jack, the guy whose room she snuck out of.

After agreeing they are absolutely not interested in each other, Jack and Hallie realize they're each other's perfect wing-person in their searches for The One. They text each other about their dates, often scheduling them at the same restaurant so that if things don't go well, the two of them can get tacos afterward.

Spoiler: they get a lot of tacos together.

Discouraged by the lack of prospects, Jack and Hallie make a wager to see who can find true love first, but when they agree to be fake dates for a weekend wedding, all bets are off. As they pretend to be a couple, lines become blurred and they both struggle to remember why the other was a bad idea to begin with.