In the end, it doesn't really matter what their excuses are for discarding us... .their brains and lives are so disordered... .
I have a bit of a different take on this.
Once, I had a girlfriend and I called off the relationship for something that she did (hacking my email - final straw). She accepted the end, but wrote me to tell me what I needed to do to be a better person. I had three thoughts:
1) Its inappropriate to tell someone to fix themselves when a relationship ends (by us or by our partner) because we have a very biased and emotional view. We shouldn't do it.
2) It's not very mature to take breakup comments too literally or consider them a fair evaluation of us. Typically the person saying them is much more concerned with themselves at this time and what they say is driven by a lot of things like guilt, not wanting it to be awkward, not wanting a debate, not wanting tears, venting frustrations, wanting a hard stop (or a soft one), posturing for a new partner, selling themselves on the idea, escaping their own bad relationship contributions, etc.
3) Do relationships even end for tactical reasons (other than infidelity, or physical abuse)? Falling out of love, devaluing, wanting a different relationship are deeper and broader considerations that drive breakups that we often can't really wrap our hands around. No one breaks up because "you don't like Christmas".
The first time my exBPD ended our relationship she told me it was because I was passive aggressive, not a happy person, didn't appreciate her, was too critical of her, didn't buy her an engagement ring (in the first month of dating), didn't put her on my checking account (again, first month) and didn't like Christmas (no really - she said that. I like Christmas).
I then found out she was cheating on me.
And so all the other reasons probably didn't mean anything - they were just more respectable reasons than I'm cheating on you.
Why was she cheating? Something was missing and so she jumped thinking she would find it in another man. What was missing?
If you think hard enough about all the fights, you will figure it out. It will make sense. It may not be mature thinking, but it will make sense. Maybe your relationship didn't live up to the idealization that brought you together and she saw that possibility in someone else.
The answer is more likely on that level.