I dont know what the piece is called but it goes on the back of my front load washer and it seperates the hot water from the cold water and its cracked

Are you referring to the water valve assembly? If so, you can purchase a new assembly. Check with a parts distributor. You will need the brand and model number.

Unplug the washer. Turn off the water supply (hot and cold) to the washer and disconnect the hoses at the washer (there is no need to disconnect the hoses at the wall). Make certain that you replace the hoses correctly on the new water valve with corresponding hot and cold hoses coming from the wall. Disconnect the wire harnesses to each temperature (hot and cold) on the water valve. The harnesses should be color-coded. Replace them correctly on the new valve. Turn the water supply back on and plug in the washer. Run a small water level while testing different temperatures (hot, cold and warm). Check for water leaks and proper temperature.