Ingenious by Barrie Farris

In a dystopian world ruled by women, brilliant but awkward Cadet Quiggs Fallon has a bright future. Academically gifted with a brain like the ancestors, he’s well on his way to figuring out how to kill the sentient vines overtaking the land, earning him—a male—an unheard-of seat in the Assembly of Ruling Mothers. And with an inheritance and an impeccable pedigree, he’s engaged to marry the governor’s daughter after his graduation from the academy.
Instead, one moment changes everything. Caught in a compromising position with his loyal-to-a-fault friend Beau, his plans are derailed. Thrown into the concubine lottery, Quiggs draws the name of the fiercest warrior in the Triangle—Commander Max Bronn, whose feral bloodline denies him the right to have a wife.

Max’s delight with winning a male concubine to substitute for a wife the next three years cools down when he learns he’s stuck with Quiggs, an untrained, gawky genius who is thoroughly pissed off at his fate.
And why is an assassin stalking Quiggs?
The reluctant attraction between Max and Quiggs soon burns hotter than Quiggs’s new fuel paste as political intrigue, danger, and the rules of society threaten their lives, and their budding romance. Now it’s a battle to save the world as they know it…or create a new one.
Adventure, science fiction, and romance come together in a slow burn that heats up with every unexpected twist and turn in this first book of the Ingenious series.

Look elsewhere if you want heroes jumping into bed by the second chapter. If you want a fun plot with m/m romance only when a scene justifies it, this science fiction thriller is written for you.