One Fiery Summer by Ashley Zakrzewski

High school crushes run into each other after a two decades apart.

Lincoln, an anesthesiologist at a children’s hospital in Houston, dedicates his life to his work and volunteering, leaving little room for romance. However, after running into the girl that got away at their twenty year reunion, her presence ignites a flame that never truly extinguished.
Heather, a recently divorced software developer, returns to Lawson Ridge seeking solace. She has emerged from the ashes of a failed marriage, seeking a fresh start in the place that had once been her sanctuary. The more time she spends with Lincoln, the promise they made before they went their separate ways all those years ago comes flooding back.

If not married or in a committed relationship by thirty-five, they would meet back up and give it another shot.