Hello, I have a Delta single-handle shower/tub faucet- model number: 1343-NPS. Last night, during my shower, I turned the handle to turn the water off and nothing happened. My shower kept on; the handle did nothing. I had to turn the building's water off in order to get the shower to stop. I took the handle off to look for something suspicious, but didn't find anything so I turn the water back on for the building. The handle then worked normally turning the water on and off.
Since then, there has been a constant drip from the faucet and if I listen close to the wall, it sounds as if the water is still on slightly even though it's turned all the way to the off position.

Please help? I don't know how to stop the dripping. Thanks in advance!