There are quite a few. 'Outlander' by Diana Gabaldon has a complex and grand love story between Claire and Jamie. Their relationship spans different times and cultures. 'The Bridges of Madison County' is another. It tells the story of a brief but intense love affair that is more about emotional connection than physical. 'Anne of Green Gables' also has a lovely love story in the later books as Anne grows up and finds love, in a very sweet and innocent way.