PieMan, my belief is that dating is about finding your Mr/Miss Right. It's not about spending time with a wrong person and trying to make it OK.
In your case, this relationship has clearly turned to shit. It's not your place to try and explain to her why she has to get over or accept the things you've said about your ex. These are her thoughts and she's entitled to them.
However, is it exactly your place to enforce your own boundaries. If this involves telling her that you will be unable to continue with her because she won't let go of this issue, then go for it. It's your place to say that you no longer want to bother with a complaining girlfriend.
It's time to give her some marching orders. If she doesn't like being thrown out, that's her problem to solve. Remember, if she hadn't been such a complaining, unforgiving bitch, she wouldn't be in the situation of having to find somewhere else to live.
There will be many more girls for you yet. You'll have great experience and some not so great ones. And hopefully you'll learn to quickly recognise when to walk away.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.