No. Staying with a cheating girlfriend is not a good idea. Trust is the foundation of a relationship, and once she has cheated, that trust is broken. It will likely lead to more pain and insecurity in the future.
One sign is secrecy. If she starts being very secretive about her phone or where she's been, like always taking her phone to the bathroom or not sharing her location. For example, in a story I heard, the cheating girlfriend would never let her partner see who she was texting.
One story I heard was that a guy noticed his girlfriend was always on her phone late at night. When he finally got a chance to look, he found flirty messages with another guy. She had been making plans to meet up with this other person behind his back.
One sign could be that she becomes overly secretive about her phone. For example, she always takes it with her everywhere, even to the bathroom, and gets very defensive if you ask to see it.
First, they should try to have an honest conversation. Just sit down and talk about what they've noticed and how it makes them feel. If she doesn't admit it or continues the bad behavior, it might be best to break up. It's not healthy to stay in a relationship with someone who cheats.
If you suspect your girlfriend is cheating for the first time, the first thing is to stay calm. Don't jump to conclusions right away. Try to have an open and honest conversation with her. For example, you can say something like 'I've noticed some things lately that are making me a bit worried, can we talk about it?' Maybe there are misunderstandings that can be cleared up through communication.
One cuckold fantasy story could be about a man who discovers his girlfriend has been secretly seeing another man. Instead of getting angry immediately, he decides to watch from a distance, feeling a strange mix of pain and arousal. He starts to question his own feelings about love and possessiveness.