Dating a different guy and having an affair with another

In this problem, a young lady who have been in a relationship for like three years but the relationship is a long distance relationship. Still in the relationship she met another guy who she started an affair with not minding who her boyfriend is. He is a kind of person that monitor her movement, he sends people to spy on her, but she still went on having an affair with this guy and later started developing strong feeling for the guy she Is having an affair with. Now the problem is, her boyfriend is aware of the affair he even called the guy and warned him. Should she confess to her obsessed boyfriend and stop the affair or continue with the affair and not tell him.