Mike Rosenberg (aka Passenger) wrote this sad song about an ex-girlfriend. He told VH1: "There's a line in the chorus, 'Four will not wait for three, for three never waited for two,' and I guess it's saying there's an inevitability (to breaking up)."
Melandria from UsaI should clarify... That's the number of the letters in the words.
Melandria from UsaHe says "four will not wait for three, for three never waited for two, and though you will not wait for me....." The last part is key in translation. Four =love. 3= you. 2 =me. Love wont wait for you. You never waited for me.