What does the song "si volvieras a mi" by josh groban mean?

whoa. im not going to bother writing what it all means but the name of the song is "if you'll return to me". the song is basically about someone who has left someone else in a romantic relationship and the singer is saying that if the person came back to them it would be a miracle and it would all be good blah blah blah. but then at the end the singer says (last 2 lines)"but today you're leaving and there is no way to go back".