Meaning of "flipped on me"?

Hello everyone. I am reading a novel, and I came across this expression. Could you please let me know its meaning?

No doubt about it. I’ll be alone all day and learn to look things squarely in the face. It may not have much to do with her. It had to do with wanting, and waiting, and hoping, and never knowing why or what I wanted. And this creature made of flesh and blood and a will so strong it could bend a steel rod simply by staring it down, was she another metaphor, an alibi, a stand-in for the things that never worked out, for what draws close but never yields? I was drowning, not swimming to Bellagio. I was on the outskirts of things, and being on the outskirts of things was how I lived life, while she . . . well, while she’d simply flipped on me. Yes, that was the cheap, petty, sordid word for it: she’d flipped on me. From extreme this to extreme that. Tit for tat.

- André Aciman, Eight White Nights, Sixth Night

This is a novel published in the United States of America in 2010. This novel is narrated by the nameless male protagonist who meets Clara at a Christmas party in Manhattan. Now the protagonist is thinking how Clara had "flipped on" him.

In this part, I wonder what the underlined expression means.

I learned in the dictionary that "flip (verb)" can mean "to become highly excited or irrational", but I am not sure whether it can fit into this context.

Also, I am curious to know how it is "cheap, petty, sordid word" to describe the situation... Is there any "sordid/petty" nuance to the word, perhaps...? o_O

Thank you very much for your help.