Morgen Prince - Deep Magic, #4

Duhywynt's only weapon against the world will cost him everyone he cares about. Duhywynt plans to spend his summer catching the legendary Ceffyl Dwr and swapping make-up tips with his best friend, Myfanwy-until he discovers his older brother has traded his morgenau heritage for mortality. Myrhydion is far more concerned with Duhywynt's lack of a social life than his own impending death. Duhywynt will do anything to avoid losing him for ever, even if that means faking a friendship with Drew, an annoying tourist holidaying in Aberdaron.
As Drew's fascination with Duhywynt grows, the prince discovers the deadly legacy of his morgenau heritage. Worse, he risks losing his relationship with Myfanwy-a relationship with depths he is only beginning to understand. Duhywynt knows nothing good can come of having feelings for a human. But can he really say goodbye to Myfanwy forever?