My faucet won't turn off?

On my bathroom sink, the left faucet handle seems to be very loose or not gripping. It's not coming off or anything, I just don't feel any tension when I turn it. Now the water is coming out nonstop and I cannot stop it =( It's 9 30 at night and I don't know what to freakin do about this.

long bathroom sink with two faucets