If the abuse isn't physical, it isn't really so serious. We know that words can wound more deeply than blows. Emotional abuse kills the spirit. Furthermore, physical abuse is always accompanied, and often preceded, by emotional abuse. At the extreme, emotional abuse can cause physical illness, loss of the will to live or death by suicide.
Abusers are generally unpleasant or angry people.
I could certainly tell if someone were an abuser. If the abuse is kept quiet, it won't affect the children. Children always know when something is wrong. Spouse abuse has demonstrable physical, neurological, emotional and social effects on children of all ages, including infants. If a spouse is abused, she or he has no choice but to get a divorce.