This was written around 1960 by Felice and Boudleaux Bryant (an interesting songwriting team I’d never heard of before) and made a hit then by the Everly Brothers. But the versions I care about are by Emmylou Harris, especially her version with Gram Parsons.
It’s about the simplest country melody imaginable, sung super slow, so the lyrics are few: Oh, these sleepless nights / Will break my heart in two. I’m really hard-pressed to pick between Ms Harris’ solo version on Pieces of the Sky (a wonderful collection, by the way) or the collaboration with Gram Parsons on a Flying Burrito Brothers album also called Sleepless Nights, which features her on several songs (extra-wonderful). The Emmylou/Gram harmonies are exquisite (granted, Emmylou/anyone harmonies usually are), but on Pieces of the Sky, Emmylou takes the song on very much alone, with an unusually spare arrangement. They’re both real weepers.
Links · Spotify playlist. Solo on Pieces of the Sky: Amazon, iTunes, Spotify. With Gram on Sleepless Nights: iTunes, Spotify. Amazon. The only live video I can find is Emmylou with the “Milk Carton Kids” (and Steve Earle sitting in) which is pretty meh.