Baby for the Grimlock General by Aurelia Skye

She’s been drafted to be a surrogate for the alien.

Violet Jones discovers she’s been matched to a Grimlock general. She’ll accompany the huge alien general to his home world. She only has to give him a year to woo her and act as his surrogate before she can walk away. At first, she’s sure she can’t give the massive alien what he wants, but he’s completely contrary to what she expects. He’s tender, caring, and obsessed with ensuring her pleasure and ability to accommodate him. Soon enough, the idea of leaving him seems crazier than the possibility of staying.
Seven years ago, the Faction agreed to save Earth from the Vorathan invasion in exchange for Earth women giving them one year of proxy rights to act as a surrogate, since the aliens of the Faction faced a dwindling population. With the Vorathans feared throughout the galaxy as bloodthirsty, vicious marauders, the Earth’s government agreed.
That doesn’t mean the women did.