On the real though you guys are still young as fuck. Thinking you'll be getting married, being in love before hitting adulthood, cutting over petty shit, its all a bunch of high school nonsense. Trust me it seems important at the time but when you reflect in a couple years you'll be like wow i've grown up a lot I was simple as fuck back then. I can tell you're still very much a child by the way you post and it seems that your girl is very much a child too by the actions you describe, the truth is you guys both don't know shit and are niave as fuck with much growing too do. If you were an adult I would say hands down dump her instantly, at your age, honestly just do what feels right and don't get your panties in a bunch. But if you do decide to dump her, don't front like shes your special one, your one and only, at your age thats true like one out of ten thousand times, and given the nature of your relationship, your odds are more like one in a million. Dumb little girls who cut and are sexually confused aren't worth tripping over b.