That PEX plastic elbow should have had a cinch/pinch band on the part that sticks up just like the one on the end with the red PEX. If it did have a clamp it either wasn't pinched correctly or often those inexpensive plastic elbows simply don't hold under the pressure of cinching the clamp.
The clamp can not be reused.
You didn't show a photo of the piece of PEX that connects to the elbow (and goes to the faucet) but you should be able to see from a marking on the PEX if a clamp was ever installed or possibly missed somehow.
It is also possible that a piece of braided white hose connected to that elbow held on with a screw type hose clamp.
Until we'd see the other piece that attaches to the elbow we are speculating.
Did you winterize your rig?
Maybe it froze and pushed the line off the elbow or broke that elbow?
In any case I would replace that plastic elbow with a good brass PEX elbow and two new PEX clamps. You'll need a PEX tool to compress the clamps. The tool can be rented at places like Lowe's and Home Depot or bought on the internet for $25-30.
PEX tool with clamps = $24.33
If there was no hose attached to the broken elbow then you'll need a fitting like this...