Erectile dysfunction has two different reasons behind it - medical or psychological. If he is medically fit (no history of long standing illness -
diabetes, hypertension,
thyroid problems, high cholesterol, low
testosterone hormones, smoking, drinking ) then most likely its psychological cause. In both case depending on root cause this condition can be treated easily with proper counseling, techniques and medications. Consult a qualified psychiatrist /sexologist near you or online for detail discussion and evaluation so that treatment can be suggested.