I think she is cheating on me!

I have been trying to break up with my girlfriend for months because I think she’s been cheating on me, but I don’t have proof. If I tell her I suspect her, she won’t accept that as a reason. I am frustrated because I don’t even like seeing her or chatting with her, but I’m forced to because we are supposedly together. Her family and friends think we’re a great couple and always invite us together for every party or occasion so I can’t avoid her for long. I am starting to get angry and have arguments with her all the time because I feel trapped and can’t get out. How do I break up if I can’t prove she is not being faithful?
There appear to be bigger issues here than trust. You say you can’t stand to see her or chat with her, and feel trapped, which points to a breakdown of this relationship any way you look at it. If you are looking for evidence of her cheating on you, it’s because you don’t have faith in her, without which there is no future even if she isn’t cheating on you. The most sensible thing to do is talk to her about how you feel, with or without any proof, because she needs to know that your heart isn’t in this anymore. Staying in a relationship because of family and friends is the easiest path to resentment, because this is about you and your girlfriend first, no one else. Keeping up appearances makes no sense to anyone after a point, and will harm not just the two of you, but everyone else who believes you are in a healthy relationship. Speak up soon.

Should I tell my parents about the boy I am dating even though I know they may forbid me from seeing him? I want to be honest, but don‘t want to lose him.
That depends upon the bond you share with your parents and how open they are to trusting your judgement.