If a bird is going to cheat on you she will, you wont stop it. Being para and annoying her will only make he more likely to do it as other blokes will seem far more fun to be with than you.

If she is asking you to chill out, then do it, if she flee's then she flee's she would have gone anyhow.

Your only young, she is unlikely to be your life partner so enjoy some nights out and nuts in.