Have you found that person? I believe there is only one person that will ever truly make you feel this way. and once you have you will never feel that way again about anyone no one will ever compare again
This poem says to not give your everything to certain people. Many of them are always changing and once they do, it can hurt you. It tries to explain to not get too comfortable with some people since the ending result can leave you with a painful memory.
That's where you messed up. You gave them the opportunity to picture a life without you, by being inconsistent. So when they got the strength, they walked away without looking back. No not walked away, they learned to move on.