You and Enzo have been together for 3 years. (You are also a vampire) Klaus makes you turn off your humanity switch by compelling you to turn it off. At first you resist, but then he screams at you to turn it off and the compulsion takes hold. You shut off your humanity and it stays off for 6 months. Enzo and everyone else does everything in their power to bring you back, it takes a long time. They do get you back.