The Time Traveler's Wife by Audrey Niffenegger #1

The pair met when Clare was just six and Henry thirty-six, and were married when Clare was twenty-two and Henry thirty.

Impossible but true.
Soon to be a major Sky TV series, The Time Traveler's Wife is the international bestselling novel of a time-altering love. Henry is a librarian who suffers from a rare condition where his genetic clock periodically resets, finding himself pulled suddenly into his past or future. Meanwhile, Clare is an artist waiting all her life for her great love Henry to appear. In the face of this force neither can prevent nor control, Henry and Clare's struggle to lead normal lives is both intensely moving and entirely unforgettable.
'Dark, unpredictable, incredibly clever and a modern romance' Grazia