i lol'd
to the OP: i think you should just deal with the fact your girl cheated on you with a guy with a massive dick. he was probably better in bed than you, gave her loads of multiple orgasms and made her squirt so hard she resulted in getting so dehydrated she needed to have a chilled isotonic beverage and sodium capsules. not only that but chances are the guy she shagged with a massive knob was probably a much better person in general, was a hell of a lot less paranoid, more charming, witty and good looking. he probably flossed twice a day, had a good job, a great car and an amazing penthouse apartment....
even if the above isn't true your far too paranoid to deal with this girl again so maybe just drop it?