The Guy Next Door by V.C. Lancaster

Kez is a Teissian refugee living in San Diego in the year 2267, working at the Department of Extra-Terrestrial Immigration, and he doesn’t like much. He doesn’t like Earth, he doesn’t like humans, he doesn’t like his job, and he definitely doesn’t like his bubbly next-door neighbour, Bia, who is convinced they are meant to be together. She’s too young for him, their personalities are completely incompatable, and back on Teiss, her people kept his as slaves. No matter what Bia says, it’s obvious to him they couldn’t be more wrong for each other.
Because Kez is keeping secrets. On Earth, he’s been able to redefine himself, and escape the difficult life he was forced to lead on Teiss. He is hiding the fact that he is mixed-race, and that he hasn’t been able to shake a nasty habit of taking other people’s things no matter how hard he tries. And letting Bia into his life would risk exposing all of that.
But despite how she was born, Bia was raised by Kez’s own people. She isn’t like the others, and as he gets to know her, he uncovers a lonely and lost female just trying to find a place to belong, a place he can give her, if he dares. When Bia needs his help, he can’t say no. He just has to make sure that their first time is also their last, because he won’t risk everything on the chance of a mate, and he won’t let her throw her future away on a male like him.