Skythane. Liminal Sky: Oberon Cycle, #1

Welcome to Oberon, one of the seven wonders of the Common Worlds-a perfect half-sphere of a planet that defies the laws of physics. Jameson has just arrived on this strange world in search of a rare psychoactive called pith. His local guide, Xander, is a handsome, cocky wing man with a troubled past, who guides him into the wilds on a quest to find the source of the mysterious substance. As the world starts to fall apart around them, they race to avert a cataclysm while fighting their mutual attraction, and travel beyond the bounds of reality to discover the secret that binds them together.
They have no idea what's coming next.