Chasing Earth by J.M. Link

Tori knows Aderus sees dealing with Earth as necessary to an unlikely, but last-ditch effort to save his world, as she tries to bridge the gap between two vastly different species while proving to him she’s more than just some unimpressive human. But her fascination and his frustration have led to an attraction she’s unprepared to handle. Or more precisely, the consequences of acting on it; which not only involve changes to her body, but struggling with what the fierce Askari inspires. And what’s actually possible between them.
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Aderus never imagined a creature like Tori would be what he has come to crave, even over his own kind. The sentiments she provokes perturb as much as they invite and entice him and understanding her proves a separate challenge. But when his actions result in an unintended threat to the balance of power in a fragile alliance between their two races, he is forced to weigh his trust in her against the only thing that matters to him. Or so he thought.