The tale of the broken heart
A heart isn't made of flesh or stone. It is made of glass, with a dark-red, thick liquid inside.
The glass is much resistent. It can fall and chip, but its very hard to break it completely.
Once one part is chipped, it can never return. It can be glued and taped, but the heart will never be whole again.
A heart that is chipped one too many times becomes weak. And by doing so, easier to break.
Once it's broken, its blood runs away, and so does love - being it an essential item to the liquid. It can no longer return. It is now sewage. Gone.
The glass can, however, be glued back. But again, it will never be the same.