Michelle,
 
The enemy will try to attack believers whenever possible. When this man broods about this situation with this woman , it leaves him open to attack.  Calling on Jesus's name drives away the attacker.
 
This is an issue I've been dealing with also. My boss ( who has recently been fired ) was the kind of person who demoralized everyone around her. But I left myself open to attack by brooding on it and depressing myself, instead of praying and trusting God to take care of the situation like I should have.
 
It doesn't mean he is possessed, but it means that the devil has found a vulnerable point. He needs to get rid of / let go of the pain he feels.  Anger is an open invitation to the devil.
 
My boss called herself a Christian too. That doesn't mean she really was a Christian. Everytime I worried about what she did to us , as long as I kept thinking about it over and over again, the devil used that opening to attack.
 
Praising God, playing gospel praise music , and thinking about good things help a lot.