Short story from the 80's or 90's, I saw someone asking about this on another forum but never got an answer. I've been curious ever since.
The story is set in a decadent future where everyone lives forever and mostly they go to parties. Guy meets a girl at a party, suggest he start at one side of an asteroid and digs a tunnel by hand to her, while she waits in a hollowed out space and creates a beautiful garden while waiting (robots take care of all mundane life support stuff).
So he digs for 100 years, makes it through to her chamber, they have a long romance, and when they've had enough they go back to civilization. The robots bury everything and return the asteroid to the way it was. Then they run into each other at a party and she overhears him proposing it to a different girl. That's when she says, "You've done this before."
This is the original post, for those curious (though I've reposted all relevant info): https://www.reddit.com/r/tipofmytongue/comments/21004u/tomtscifi_short_storyeveryone_lives_forever_man/