Emotional and mental abuse is just as serious as verbal and physical. As mentioned above, your friend needs to get out while she can.
Most of us who have been in situations similar understand the " I can't leave I have no where to go", "what about my children, I can't provide for them", "he's going to change, he said so".
They can leave, the children will be better off and no, he will never ever change. EVER.
Make the calls, find a support system and get her out. That's the best way to help.
And for the record, people who distrust their partners for no apparent reason do so because of guilt of their OWN actions.