The Rule Book by Sarah Adams

College exes break all the rules when they reunite years later in this enemies to lovers, second-chance romance, the highly anticipated companion novel to the TikTok sensation The Cheat Sheet—from the New York Times bestselling author of Practice Makes Perfect.
Nora Mackenzie’s entire career lies in the hands of famous NFL tight end Derek Pender, who also happens to be her extremely hot college ex-boyfriend. Nora didn’t end things as gracefully as she could have back then, and now it has come back to haunt her. Derek is her first client as an official full-time sports agent and he’s holding a grudge.
Derek has set his sights on a little friendly revenge. If Nora Mackenzie, the first girl to ever break his heart, wants to be his agent, oh, he’ll let her be his agent. The plan is simple: make Nora’s life absolutely miserable. But if Derek knows anything about the woman he once loved—she won’t quit easily.
Instead of giving in, Nora starts a scheme of her own. But then a wild night in Vegas leads to Nora and Derek in bed the next morning married. With their rule book out the window, could this new relationship save their careers or spark the romance of a lifetime?