The Twin Kingdoms
The long-lived elves mark the entirety of the southern forest as their home. An ancient and dignified race, they are occasional visitors to the Human lands, finding the short lives of the other races to be vibrant and joyous, even in their most sorrowful moments. An Elf meeting a Human and falling in love occurs often enough that it is a common thread in many stories and song.
In every occasion, the Elven partner chooses to settle with their Human lover, as a short-lived Human living in among the long-lived Elves would not have been comfortable (even though, and possibly because of, the Elves would have done everything they could to make such a Human comfortable living with them). The Elf will remain with their love until they die, and then immediately depart for their Elven forest once more.
Any product of such a union is greatly admired in human society, with the attractive strangeness of the melding of the two races combined with their extended lifespan making them fascinating to other humans. To Elves however, they are looked on with sympathy and pity, like a disadvantaged child, though treated with all the respect their Elven heritage means they are due.