Alienate by Nova Noble

Zartag Zagan, leader of the Neander Beasts, engages in a losing war to defend his people’s right to repopulate Earth. When Zinthrodite, leader of the Zincmeda, offers him her powerful fleet of warships, he agrees, even though he has avoided the wickedly smart woman for years.
But deals have two sides, and the price Zagan must pay for his people’s freedom is a personal one. He must marry Zinthrodite, saving her from assuming the throne on her own planet.
Space battles, betrayals, and enemies-turned-fake spouses lead to a stunning conclusion neither Zagan nor any of his people could imagine.