Alastair Macleod 
The Return 

This story is a sequel to ‘Leaving, ‘ in which Alanna, a visitor from Zarthon lands on a North Ronaldsay, a small island threatened by rising sea levels. Alanna leaves with Callum, the last remaining inhabitant, to return to her home world. They begin a relationship.

But Callum soon finds life on Zarthon somewhat lacking and he misses his home on the island.