He has a disorder causing unpredictable travel through time. She marries him, and must cope with his frequent absences.
With the release of the movie version of The Time Traveler's Wife, Audrey Niffenegger’s 2003 debut novel that became a bestseller, you may enjoy reading these other titles featuring love challenged by time travel.

Dreams of Stardust by Lynn Kurland FIC KUR
Journeying to Seakirk castle to research jewels for his latest creation, Jake Kilchurn is transported back in time to medieval England where he finds the woman of his dreams in Amanda de Piaget, but the constraints of time threaten their love.

The Immortal Highlander by Karen Marie Moning FIC MON
Stripped of his immortality and rendered invisible by a curse, Adam Black seeks help from Gabrielle O'Callaghan, the only woman who can see him, but their subsequent romance is challenged by a dangerous conspiracy.

A Knight in Shining Armor by Jude Deveraux FIC DEV
When Dougless Montgomery is abandoned by her boyfriend at a church in England, her tears of despair conjure up a sixteenth century knight: Nicholas Stafford, Earl of Thornwyck.

Knights by Linda Lael Miller FIC MIL
In medieval England, Gloriana, Lady of Kenbrook, awaits her husband, Dane St. Gregory (to whom she was married as a child) only to be stunned when he returns with a betrothed, and finds herself thrust seven centuries into the future, with her love for Dane her only hope.

Outlander by Diana Gabaldon FIC GAB
Hurtled back through time more than two hundred years to Scotland in 1743, Claire Randall finds herself caught in the midst of an unfamiliar world torn apart by violence, pestilence, and revolution and haunted by her growing feelings for James Fraser, a young soldier.

Portrait of a Bride by Tracy Fobes FIC FOR
A painter with the power to bring his feminine creations to life loses his masterpiece and must travel to modern-day Philadelphia to retrieve her, in a romance filled with adventure.

Tall, Dark, and Kilted by Allie Mackay FIC MCK
Arriving at Dunroamin Castle in Scotland, jeweler Cilla Swanner finds her plans for some rest and relaxation interrupted by the ghost of a Scottish knight, cursed to roam the Earth forever, pleasing a different women each night with no hope of true love--until he meets her.

Time and Again by Nora Roberts FIC ROB
After time traveler Caleb Hornblower crash-lands in the twentieth century, he relies on Liberty Stone to help him survive; and Jacob Hornblower heads back into the past to rescue his stranded brother, only to find himself falling for Sunbeam Stone.

Tumbling Through Time by Gwyn Cready FIC CRE
While shoe shopping, Persephone "Seph" Pyle finds herself in 1706 and in Phillip Drummond's arms, a pirate with a striking resemblance to a modern-day colleague.

Secrets of the Highwayman by Sara McKenzie FIC MCK
Two centuries ago, Nathaniel Raven was murdered. He now has one opportunity to uncover the truth of that night, and Melanie is the only woman who can help him.

Son of the Morning by Linda Howard FIC HOW
Grace St. John is translating manuscripts involving the Knights Templar when her husband and brother are murdered. Grace flees and finds herself transported back to fourteenth century Scotland, where she falls in love with Niall MacRobert, the guardian of a treasure.

Viking Unchained by Sandra Hill FIC HIL
Searching for his little boy, 11th century Viking Thorfinn lands in modern times, where he stumbles upon a dead wringer for his cheating ex-wife.