This is quite possibly the most beautiful song ever written and performed.
From 1967, here are The Association, with a pure and simple tribute to undying love and patience. But as simple as the lyrics are, the song is very musically dense, with multipart harmonies throughout and a six piece band. I encourage you to listen more than once.
What I love about this band is that, nearly 50 years later, they're still together and still playing this song. They've lost a little bit in the voices - age will do that to you - but not much, and the harmonies are still there. This performance is from 2012.