Some people don't understand the meaning of honesty and cheat the other person without any hesitation. It's bad either to cheat someone or to get cheated by someone. After getting cheated by someone you feel like a betrayal and you can never get out of that anger. Because, the thing frustrate you is that how anyone can run to someone else if you are there for the person all the time.
Similarly, a girl cheated her man and then tried to patch up with him. See, how the frustrated guy conversated to her:
She messaged him for apology in very decent way.
The guy put all the questions which were bothering him.
His anger is genuine, any honest guy'll feel in this way.
You can never imagine what is going on in a girl's mind.