Why has my libido disappeared?

Rarely for one reason - usually several stacked: exhaustion, stress, hormonal shifts, medication (antidepressants and some contraceptives are frequent culprits), an unresolved thing in the relationship, or simply a body you don't feel at home in. Desire is the canary in the mine - first to go quiet when anything is off. Start with sleep and stress; see a doctor to rule out the medical layer, especially if the change was sudden. And be kinder than you're being. It's a signal to listen to, not a fault to fix.