She has lost respect and interest in you. Shes suppose to be ur girlfriend that means she suppose to represent u. Speaking only good things about u infront of u and behind u. When she start telling lies, and going behind u who know what else she will do. This person is no longer trust worthy.. This is not loving or caring of her. Meaning she dose not care about how u feel or how others will look at u. And she dose not love u enough to forgive u so thats where the lies springs from. Hope yall can work it out tho or go ur separate ways