Wrong Number, Right Soldier by Tarin Lex

Saylis is a soon-to-be Language Arts teacher with everything she needs—except the bravery needed to step out into the world. She gathers just enough nerve to call the rando who slid her his business card, something she definitely would not have done if she knew she’d accidentally be calling Kuwait.
On his second deployment, Trey Rivers has come to expect the unexpected. But that never included a surprise like Saylis. She’s sweet, highly intelligent, with those blue eyes as bright as her future. In other words: his complete contrast.
If he were a smart man, he’d let her go. But she’s holding on tight, and he’s already addicted. Obsessed.

This could be the best bad decision either of them ever made.