question about boyfriend cheating

it's an example (fake name, lady name is Jenny and guy name is Carlos).when the couple was into relationship for the first time. The couple had been together for 2 month or less and Carlos is start to the less call or text or video chat and barely talk to Jenny. Jenny start feeling something not right and find out his cell phone that he had been talk to other girl and tell other girl( oh I miss u, been thinking of you, blah blah). Jenny find out more information then talk to Carlos about it and he start denied and denied. Finally Jenny decide to talk to that girl who he had been mess around with. Girl tell a whole story what's happen between her and Carlos. So, what she should to do leave him or stay with him and give him other chance?