I think my girlfriend is an innately bad person.
Why are you so sure that she is a bad person?
You've never given yourself a chance. I've tried to be positive for months and now we're broken up. It's my chance to move on with my life and alone is better than with her.
While it is good to move on from a relationship that you think is no longer working for you, it's not appropriate to call your ex an innately bad person as it indicates that she is irredeemable. Speaking ill thoughts like that about your exes isn't socially acceptable as it makes you out to be negative and judgmental. You should try to instead think that your ex was just not compatible with you rather than having a character flaw that doomed the relationship.
I regret that I'm going to let it end on bad terms because I care enough to let her know if she changes her ways someday she can come back but right now she has a lot of growing up to do and I have a lot of personal changes I need to make.
I think that you should just try to forget about it and move on. It is not kind to speak bad on your exes. It looks better if you just move on with life.