Diary of a Wimpy Kid: The Third Wheel

Diary of a Wimpy Kid: The Third Wheel is the seventh book in the Diary of a Wimpy Kid series by Jeff Kinney. 

A Valentine's Day dance at Greg's school has turned his world upside down. As Greg scrambles to find a date, he's worried he'll be left out in the cold on the big night. His friend, Rowley, doesn't have any prospects either but that's small consolation. Then an unexpected twist gives Greg a partner for the dance and leaves Rowley the odd man out.