Why does my ex best friend want to ruin my life now and is she wrong or what!?

i mean to the extent of saying i have stds and im a drug addict! i mean real low LOW stuff. and more perplexing is that shes the one whith -ish dirt that i could tell, but apparently that doesnt matter to a stone cold liar if she can out-lie her way. some people have told me she is very jealous, and also that people like that would rather show you some pain and go down in flames than to be forgotten quietly. can you tell me why someone does this? instead of just being like "ok, were parting ways, farewell"?