Pledge love eternal,
And you'll soon discover it
Probably won't last.
This is a song by Ralph and Carter Stanley, one of those high-and-lonesome bluegrass tunes about abandoned love.
In short:He sits on the river banks, accompanied by the lonely wind and the high water. He's too lonely to cry and has no one to love or kiss him goodnight because the woman he loves left him this morning. Once they swore to each other that they would stay together and be happy forever. Then she fell in love with someone else.