Guardian Series by C. Osborne Rapley

Following an unsuccessful and debilitating experiment by the Navy, Tristan Taylor’s now reclusive and desolate life takes a shocking turn with the arrival of an alien warrior whose ship has crash-landed behind his isolated cottage.Discovering that his previously failed brain implant can interface with the alien's computers, Tristan resolves to accompany the enchanting Aesia in her quest to return to her people...little knowing what awaits him. And at what price...?