Listen to this song called "Man of the World," which was released as the follow-up single to "Albatross" in 1969. It's a slow, sad, dreamy Peter Green tune and good god it is gorgeous. Outside of compilation albums, "Man of the World" was never released on a proper album; I think the only version that you can legitimately buy right now is an alternate take, not the original single.
But man, this is a stunner, a broken-hearted love song that turns the British blues Fleetwood Mac was raised on into something far more personal. I also kind of hear it as an elegy to the '60s and the free-love era; a year later, Green took some bad LSD and quit the band, which went on to become one of the biggest in the world.
(Also: Vote for the second best Fleetwood Mac album before it's too late!)