In the manga/anime series Fairy Tail by Hiro Mashima, Zeref Dragneel and Mavis Vermillion share a tragic romantic history that spans centuries and ties directly into the founding of the Fairy Tail guild.
Mavis Vermillion was the founder and first guild master of Fairy Tail, living roughly 400 years before the main story. Zeref Dragneel was already an extraordinarily powerful and ancient dark mage, cursed with immortality after accidentally creating the death magic Ankhseram Black Magic, which killed those he loved, including his younger brother Natsu (whom he later revived as the dragon Igneel/E.N.D.).
Mavis and Zeref met when she was young, and the two fell in love. However, because Zeref was afflicted by the Ankhseram curse — which causes death to come to anyone he feels strong positive emotion (like love) for — being close to him put Mavis in constant danger. During a war involving the country of Alvarez, Mavis unknowingly cast a powerful spell (Fairy Sphere/Fairy Heart) to protect her comrades, but the magic ended up putting her into a centuries-long death-like, suspended state, effectively "freezing" her. Zeref, believing he had caused her death through his curse, was devastated, and this loss became one of the central sources of his despair and his subsequent quest to find a way to die (since immortality made his curse a perpetual torment).
Centuries later, in the main story timeline, Mavis's spirit or preserved form continues to interact with the present-day Fairy Tail guild, and her unresolved connection to Zeref becomes a major plot thread. Eventually, near the end of the series, the curse's effects are undone and the two are able to be together, dying together peacefully as an old married couple, resolving their tragic, centuries-spanning love story.