Sheltered (Innocence Lost #3)
Margot Scott

He vowed to keep her safe, but can he save her from his forbidden desires?
Poison gas. Mass panic. He was prepared for this. What he couldn’t prepare for was what happened after he bolted the door: four years trapped in a doomsday bunker with his ex-girlfriend's untouched angel, Casey. Only now, at eighteen, his innocent bedfellow isn’t so naive anymore. She's a grown woman, with a grown woman's needs.
Lying beside her every night, he doesn’t know how much longer he can keep his distance. Especially when Casey can't resist exploring her very grown-up body beside him on the cot.