Daphnis and Chloe, by Longus
Longus was a Greek, living under the Roman Empire sometime in the second or third centuries AD. Virtually nothing else is known of him, but he might have been from Lesbos, where he sets his story. This is an early Greek romance, a sentimental little story written for amusement and even as a sort of cheer-up therapy for the melancholy, and the very archetype of a pastoral.
Daphnis is 15 and Chloe 13, and they are island shepherds. Every day, they care for their flocks, pray to the local nymphs, and play music. They fall in love, but are too innocent to know what love is, so they are just kind of tormented. The story is sprinkled with dramatic incidents; Daphnis is captured by pirates (and saved by divine intervention), Chloe is captured by a different set of bad guys and saved, a terrible winter separates the two, and finally the shepherds' wealthy master arrives and it is time for all to be revealed and the happy ending.
It's a sweet little story that I've been meaning to get to for a while.