AIO I(20M) left my ex(19F) because romance books ruined our relationship

So I was in a relationship for almost seven months with a girl. She was really great, cute, nice, and smart. But she lacked self-esteem and had been pretty insecure all her life, and I was her very first boyfriend.

My girlfriend had a hard time with boys all her life; no boy ever showed interest in her. Which means that her only vision of boys, her only knowledge of boys, came from those romance books she used to read a lot, and from Korean dramas.

And that ruined our relationship.

One day, I went to pick my girlfriend up from work. She works in a clothing store. In the car, she started telling me about her day, like usual. Then, out of nowhere, she tells me:

"Oh, by the way, I saw the most handsome man of my life at work today!"

I raised my eyebrows to show surprise, but she did not notice and continued.

"Yeah, he came and asked for my manager, but he was sooo handsome and tall that I couldn't even talk to answer, so my coworker took care of him. And then, I stayed in a corner of the shop looking at him because I felt interested in him. And guess what? My manager came to me a few minutes later and told me: 'Hey, the man who just came is from our company; he will be your mentor for a few days to teach you the job a little more.'"

At this point, I was just silently driving. I didn’t know what to say. And seeing that I wasn’t giving any reaction, my girlfriend insisted:

"Did you hear? The handsome man will be my mentor."

I answered, "Well, I hope he teaches you well."

"He will! And maybe he will also teach me how to love! I really thought he was handsome."

I didn’t reply. We then arrived at her place, and she got out of the car. But I didn’t. Seeing me stay, she asked what was wrong. I then told her, word for word:

"Listen, have fun at work with your handsome mentor, but you and I are done. Forget me. Bye," and I immediately left without letting her respond.

I know it’s immature, cowardly, and stupid to leave someone like that. But still, I really felt it was a huge lack of respect.

It’s been two days since then, and she’s been sending me voice messages while crying. And it’s in these messages that I learned the truth: A man did come to her work to ask for her manager, but he wasn’t her mentor—just a customer. But since my girlfriend is used to these romance books, she imagined this entire situation. According to her, she told me this story to make me jealous because, in these books, this kind of situation often happens and makes the boyfriend jealous, which supposedly shows he cares about the girl with a "healthy possessiveness." She even dared to tell me she never thought I’d believe her story about the mentor was real, let alone take it badly. She was bold enough to tell me "a book lover or a writer would have understanded that my story was just a story, not real life !"

Seriously, who whould have understand it ? I swear I wrote our conversation the EXACT WAY it happened. Who in the world would have got it was just a story, a fake story ? And EVEN if it is, she still had those words about a man to me, and even if in reality he was just a random customer, it is a tremendous lack of respect in my opinion.

She’s begged me a hundred times to forgive her and come back, saying this whole story was just a silly mistake because of her love for books and dramas.

I won’t get back with this girl; that’s out of the question. But I’d like to know your opinion on this, whether this has happened to anyone before, and if you think I overreacted.