Michael, you're too concentrated on whether she is cheating or not instead of trying to solve the problems between the two of you. Why have you been fighting? I'd get racheted at you too if you stood "over me" when I was trying to work/play online. And why are you using her cell, what's wrong with yours? I think you're smothering her a bit?

If she's cheating or not, that will become evident at some time; work on being the best boyfriend you can be, supportive, caring, "yourself" and not on catching her out and suspecting her, etc. You have a life to live that's separate from hers and what she's doing, even if you were married to her. Concentrate on becoming the kind of man you want to be.