Sawyer by Theresa Beachman

Surviving the invasion was only the beginning.

Weapons engineer Julia Simmons is struggling to come to terms with Earth’s devastation. Driven to complete the prototype of her new weapon, workaholic Julia has no time for a relationship. She makes Ben Sawyer promise they will not fall in love, because there’s no time for love in the apocalypse, right?
Former police officer Sawyer is haunted by his past, where doing the right thing came at high personal cost. When he rescues Julia from alien attack and brings her to the safety of the underground Command Base, Sawyer falls hard for her brilliant mind and soft curves.
But events escalate and a new alien menace threatens the very heart of the previously impenetrable base. Even if they can survive the dangers closing in on them, Julia and Sawyer may not survive each other’s dark secrets.

The question then becomes, who will be the first to admit to love?