Long Distance Relationships.
you need to be honest with each other, if she likes you as much as you like her then she wouldn't cheat. Ask her delicately would she ever cheat. Be honest with her and tell her how you feel and it should settle your miss trust. maybe you where cheated on before but if you where don't focus on the negative. Think of hope happy you are together and it sounds a bit like control issues. If it was meant to be then it will be.