Sometimes a failed relationship is a blessing in disguise, no matter how much you feel that it should have lasted or worked.
When you suddenly realize that that person no longer loves you, and is willing to walk away without looking back, the feeling of failure is so thick and deep within your heart that it seems you'll never recover.
And, one day in the future, you hear about him/her or you see or hear something that reminds you of them. You think of them without that feeling. You realize that it wasn't meant to be, you would never have made them happy. And they would have made you miserable to stay. And you're glad it's over.
You smile, shake your head and heave a sigh of relief, then turn and embrace the life that you've made for yourself since then. What a blessing.