I told her (because she asked), "It was the ups and downs." That language is correct but misleading because it seems to point to her emotional highs and lows, as though a nearly decade-long relationship could fail because one of the partners is moody.
Reality was far more exhausting.
It was her punishment-by-withdrawal: stomping off for her car if she felt slighted, which, granted narcissistic personality disorder, was pretty much continual. Sleeping on the floor instead of the bed, in a huff over triviality. It was a crude attempt at control: negative reinforcement, where the message is, Cross me and you'll pay.
And it was her habitual lying, whether the "little white lies" of which she feels positively proud, or the more egregiously mean-spirited attempts at manipulation. Either way she could not be trusted, so that I expended so many of my not very copious emotional resources sorting, or failing to sort, truth from not.
And it was her enjoyment of the woman-in-the-middle attack, her love of conveying negative statements from others to the person those statements reference, then bringing the offended person's usually angry response back to the person who made the statement, like this: "My sister says you're not good enough for me." "Fine. Tell your sister to go fuck herself." Then, to her sister, "Mark says you should go fuck yourself," where sister has no context for that outburst and does not place it as a reply in a dialog. So that both parties feel attacked by the other, when in reality it was the woman-in-the-middle deliberately creating chaos. Often because she felt envy that others were happier than she.
It was her pettiness, her spite, her envy, her inability to feel joy for others, her inability to see past surfaces, her refusal to believe things exist below surfaces, her absurd pre-Feminist Battle of the Sexes notion that women and men are different species. Her untrustworthiness. Eventually, her love of things evil, including explicitly that word. "He's so evil!, she'd say, delightedly. Where he wasn't evil, he was only small, which became her own ambition. I assume because it was within her reach.
When I left her I experienced a two-year surge of energy I now see as the highpoint of my creativity and the happiest period of my life. Fueled by liberation.