What is the name of the dilemma that refers to a romance between two lovers of differing lifespans?

I'm thinking the Immortality Dilemma, if there even is a name for it. But the idea comes up in mythology, and especially in fantasy settings. For instance, Elves who, depending on the lore, may be immortal, live 1000s of years, or just hundreds. Let's say the elf falls in love with a human, and the two are devoted to one another soul and body. The tragedy that comes from watching one's partner age and die while they remain youthful and outlast them for centuries to come, and the heartache the process brings. Is there a name that already exists for this dilemma?