Most Helpful Girl
I agree, break up and find another tutor but if those options aren't available you need to tell her and show her the proof. Then see where you guys can take it from there. Tell her if that is how she feels you guys can break up and move out of each other's lives but if she says other wise then you are conflicted.
Most Helpful Guy
I'd break up with her if I was you because if she hasn't cheated on you already she will do.
She's more interested in the guy she sent that message to than you. We all have arguments but her conduct is unacceptable and I think you should walk away now before you really do get hurt because I'm not kidding man, this is a train wreck in the making.