Sort of early cyberpunk. In distant starfaring future, humans have genetically tweaked themselves so much, they don't quite look familiar. We see the "marriage" of a mermaid human to a starfarer male human - marriage is the only time they ever meet, & the ceremony is essentially an exchange of their simulation data - then each goes its own separate way, never to meet again. Whenever you want the company of another, you just interface with a machine & load the partner's data - experience all you can together, including sex! Of course, you will usually have married many times - so you have many partners' data!
Fact sheet.First published: Rogue, February/March 1966.
Note: Why is this post so short?