As traditional songs, I'd say The Turtle Dove / Ten Thousand Miles / My Love is Like A Red Red Rose and other variations on the theme.

"The tides may cease to beat the shore, and the stars fall from the sky/ but I shall love you more and more, until the day I die..."
Doesn't get more loving and devoted than that. My wife and I did actually consider having it engraved on our wedding rings, but realised it would have to be very very small.