They don't, however, have quite the narrative staying power of Cupid & Psyche, and the reason likely comes down to all their devotion occurring in absence, rather like Monk and Queen Victoria forever mourning their spouses.
Set kills Osiris and eventually cuts him into pieces (the first serial killer!). Isis goes looking for him (the first female detective!) with the help of her sister, Nephthys.
She finds him and preserves him, creating the first mummy. At this point, in some versions, Set finds the mummy and dissembles it. Isis reassembles almost all the parts! Despite some, ah, missing parts, she is able to conceive Horus.
Even when reanimated, Osiris doesn't entirely cross over into mortality. Instead, he presides over the underworld, where he becomes judge.
Historically, pharaohs eventually became associated with Osiris and actually took on the persona of Osiris when they died.
(It helps to keep in mind that the myth is extremely old and has multiple renditions.)
In any case, as one of the earliest seminal romantic myths, it falls more into Sleepless in Seattle territory than You've Got Mail--more about what the lovers do away from each other than what they do when they are hanging out together.
Romances seems to generally fall into one of these two categories: how the lovers prove their affection and undying loyalty despite separation versus how the couple gets along as the relationship evolves.
I prefer the latter but find it fascinating how old the first trope proves to be!
