I'm upset with my girlfriend because she downloaded a dating app.
That's terrible. Do you feel betrayed by that?
She has been flirting with other men.
That's a terrible situation, I'm sorry about that. Flirting with people while in a relationship definitely crosses the line. You have every right to be upset.
I'm going to file a police report against her.
She should have never done that. You have every right to be upset with her doing that while in a relationship with you.