Friend needs help.

Hello I figured since you guys have all been so helpful to me i would ask you guys. So my friend(Sam not real name) and her boyfriend(Kyle a gain fake name)have been together for 4 or 5 years not 100% sure. But they have been having a lot of problems lately due to the fact that they work completely opposite shifts. Well last week she found out that he had been "seeing" another girl(Abby). They did nothing I am friends with the other girl. (My friend doesn't know that I know her) so I asked her and she said that all her and him did was sit on the couch and watch tv and talk. When Sam and Kyle talked he told her the same story abby told me. He also immediately showed Sam all of the messages between him and abby and it was nothing sexual he blocked her on all social media and promised to never talk to or hang out with her again. Sam really appreciated that but she is still having thoughts of breaking up. What do you guys think? Should she leave or stay with him.