Darken by Clarissa Lake

Cyborg Marine Ranger Darken Wolf is coming to Earth to become a law enforcement officer in the post-apocalyptic American West and meet his genetic mate. When he arrives, she is missing.
Gina Malcolm’s best friend points him to Overlord Devlin White, from whom she escaped several years before. Darken steals into the Overlord’s compound to free her, and they flee. Of course, it couldn’t be that easy.
A fighter plane follows Darken’s sky cycle and shoots them down over the New Mexican desert. While the landing was a little rough, the bigger problem is that Darken’s CPU shuts down, and the sky cycle burns along with Darken’s only comm. He is not even sure where they are but decides going North is the best plan. It could be a very long walk.

This is only the beginning as they get acquainted and embark on a life as a couple. All they have to do is survive long enough to share a future together.