This is one of the many references used in
Moulin Rouge to various love songs in the
Elephant Love Song Medley. "Love is like oxygen.
Love is a many splendor thing. Love lifts us up where we belong. All you need is love!"
On another unrelated note, and I know that this is slightly different from the node title, but I saw a shirt the other day that said, "Sex is like air. You don't care about it until you're not getting any." That is so true about sex, but I suppose it isn't about love. You always care about love.