What does it mean when the crystal breaks?

When a crystal breaks, it usually means that it absorbed negativity from the wearer. It could mean that the crystal is done with its purpose, and that it completed the cleansing of the wearer’s energy. It is also possible that it is not programmed correctly or even that the crystal is not cleansed and charged regularly.
That being said, if the crystal breaks completely, you should thank the crystal from the heart for everything it has done for you and either throw it into the river or stream or bury it in the ground somewhere away from your living space.