UnSeal Me by D. S. Wrights, Lilith Dark

Returning for the summer to her rural home, pre-med student Joana “Jo” Mallory crashes into her teenage crush and elusive neighbor Colin Thompson.
Leaving on the spur of the moment after a family car crash that left Colin and his younger brother Jackson orphans, he joined the military and never looked back. Until now. In order to finance Jax’s Master’s degree, he has returned to dissolve his abandoned parent’s house, renovate and sell it. Or so it seems.
The once fun-loving and audacious Colin has changed in a way that re-ignites Jo’s attraction to him like a firestorm. He’s silent, brooding, mysterious and keeps to himself, but still bad luck seems to follow him where ever he goes.
After a sizzling one night stand, dumbfounded Jo ends up being blown off.
Believing that Colin simply suffers from PTSD after being the lone survivor of his team, Jo sets out to help him, just to learn a terrifying truth, that changes everything.