What's with the comments saying that Living X Ghost relationships have to be sad? Out of all Immortal X Mortal relationships it's probably the best one. Once the mortal dies they'll just stay together as ghosts. They might even be able to "physically" interact with each other even once both are dead. It would open so many doors. That's honestly a pretty neat concept.
Image if a story started with an old lady on her deathbed speaking with her ghost wife. Reminiscing of all the fun times they had and then finally slipping away. Then, she suddenly wakes up with her ghost wife grinning gleefully down at her. She's dead, now also a ghost, maybe not an old anymore either and for comedic effect maybe even confused as to what's going on. And then, with both of them haunting their house together their new romance story begins.