Your gf needs to tell you, without a doubt that if you don't stfu, she is going to dump your sorry ass. If she says anything less or she does anything to placate you, like changes her attire, then she's just going to perpetuate your need for control and next thing you know, you'll upgrade your need to control by not alowing her to see friends or family.
I hope she doesn't enable you to become the person you're starting to become... which is an abuser. Get councelling to help you within if you can't turn of your run-away-thoughts on your own.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion