My Only One by Ella Goode

Mack and Dally have known each other forever. His sister is married to her best friend. At every family function and every holiday, they’re thrown together. Everyone says that they would make the perfect couple.
And that’s the problem. No matter how many times Mack offers himself up to Dally, she runs away—sometimes literally. Good thing Mack’s determined to convince Dally that she’s not just a convenience, but the only one who will ever hold his heart.