I don't understand the song as "you don't need anyone to make you feel complete" - I think it's more about realising you're not complete. And you're lover shouldn't necessarily complete you.
If you think it as a continuation of 5 years, you could say that she is a coward too, because she was so lazy: she thought they would complete eachother and that the "completeness" would keep them together. But as 5 years also indicates: You have to fight for love.
I agree with jimmyupt.
I don't understand the song as "you don't need anyone to make you feel complete" - I think it's more about realising you're not complete. And you're lover shouldn't necessarily complete you. If you think it as a continuation of 5 years, you could say that she is a coward too, because she was so lazy: she thought they would complete eachother and that the "completeness" would keep them together. But as 5 years also indicates: You have to fight for love.