Crystals absorb, move, and hold energy. If yours suddenly cracks or breaks, it may have completed its energetic work with you, protected you from unseen harm, or released something it was holding.
Rather than seeing it as a loss, think of it as a transition. Some people choose to thank the crystal for its support and return the pieces to the earth, while others keep the fragments as a reminder of the wisdom/support it offered.
I usually thank my broken crystals and bury them under a tree or place them outside in a discreet location. 
How about you? Let me know in the comments! 
~Christine