My fiance suffers from terrible migraines. could trazodone be the cause of them?

Unlikely: Migraine is a dramatic event that may occur with stress or reaction to certain triggers. Certain foods and medicines may do this, but it is often not a clear cause. Trazadone is used with benefit in many migraine patients. She needs to explore causes and develop a thorough management plan. She needs to discuss these issues with her doctor.

Sleep apnea possible: Many patients with insomnia also have sleep apnea.... If he snores, awakes from sleep, or has long pauses in his breathing he likely has sleep apnea. Treating it will help his insomnia and may resolve his migraines.

Trazodone: Also, trazodone can exacerbate headaches in susceptible individuals such as ones with migraine history. Discuss with his prescribing doctor.