I'm grateful that the first time I read Return of the King it was a late 1950's hardback printing I checked out from the library and had all the Appendices. The tale of Aragorn and Arwen did seem that it should have been in the main tale somewhere, but I can understand why it wasn't.
Indeed, Arwen was likely not as bold and forward as Luthien was, but still....
Elf/Mortal one night stands are it seems eternal bonds.