Love and Other Enchantments by Masha Zur-Glozman

Idit, a polyglot and literary translator, falls in love with Halimi, a magnetic and philandering magazine editor. Idit, who cannot handle his indiscretions, proposes an open marriage to try and save what they've built. In the midst of a full-blown marital crisis, they take their daughter Lily and leave Tel Aviv, moving to the small seaside town of Atlit. One hot day while on a walk, Idit stumbles upon an ancient spring near the ruins of a Crusader fortress. When she bends down to drink the cool water, an old, found copper coin that she wears as a pendant dips into the spring—and suddenly she is thrust back in time—right into the arms of Jean d’Ibelin, a handsome French Crusader knight.
     She's traveled to the year 1240, the year of one of the most successful crusades in history. The noble Sir Jean—with his chiseled face and amber eyes—becomes entranced by Idit, the exotic visitor from the future. As her relationship with Sir Jean starts to deepen, Idit begins to regularly visit the distant past. Their delicate affair unfolds in parallel with the story of her relationship with Halimi, with whom she shares a beloved daughter, Lily. In the end, Idit must decide what love means to her.