I’ve read and reviewed some erotica here that features happy polyamorous relationships. I’ve been struggling, and failing, to think of any in the fantasy or YA genres. It’s definitely an area that could use more exploration. Sorry I couldn’t be more help.
Readers have any suggestions?
Check out the Wicked Lovely series by Melissa Marr. There are two polyamorous relationships, and while I wouldn’t exactly call them happy, that’s mostly because no one in the series is really happy. So like…it’s not the relationship that makes them unhappy. Yanno? The whole series features them as minor to major characters, but the two where they feature most prominently are Ink Exchange and Radiant Shadows. The poly relationship in RS is much happier than the one in INK.
The Summer Prince by Alaya Dawn Johnson is a sci-fi/dystopia that is poly-friendly, although there is some angst around the MC’s mother having more than one partner, if I recall correctly. But one of the characters is in relationships with multiple people at once and it’s tots cool.
Good luck on your search!