Should I just forget about her?

Hello everyone, I am 19 yrs old student and this is something that started bothering me lately. I will write a story that someone will maybe find stupid and tell me that I am stupid XD.
Little bit about me: as I said, 19yo software engineering student from small city, introvert,not really handsome but I wouldn't consider myself bad looking too.
The story begins 1 year ago. I still lived in my homecity, going to high school. One day I started talking to one girl on snapchat (don't judge me). She is from another bigger city. We started talking everyday, facetiming eachother (she was the girl I from my dreams hah) from time to time and one day she mentioned that it would be nice if we met each other soon. Now, this is the situation: I never had a girlfriend, heck, to me as an introvert this was something "brand new", I got attached. I was in clouds, even now when I remember it, I know the feeling(idk if it can be called love/crush or not since it was an online thing). So, I got an opportunity to come to her....but 1 month after she said this. She loved it...I guess. We continued the talk but it started to fade away during the month.
Few days before trip to her city, she said that she may not be able to meet me. I wasn't really happy tho. Still I came and guess what, we didn't see each other. After this I was really devastated and angry. Some time goes by and she contacts me like nothing happened. I guess she was trying to see how I was feeling? I brushed her off bc I was still angry at everything. From this point I was kinda in a bad mood all the time, questioning myself what I did wrong, I can say I hated myself. Some time goes by and I worked on myself, trying to get my thoughts away. I went to the gym and lost some weight, enough weight to see the difference.

Skip to last week. I am ending the 1st semester, in a another city. Unfortunately I didn't met many new people cause the class is online :/
One day I was going to class in train and guess what, I bump into her. I am sure as hell it was her,no mask, no anything. Since I remember in which part of city she lives, I was even more sure! She got in train at "right" station(I wrote right bc I don't know how to say what I want to say in English). I didn't say anything(train was almost empty). The whole ride, she looked at me nervously.
From this on I have a problem in my head. Some of you can say I am an morron or worse but that's how it is. I again can't stop thinking about what happened 1 year ago.

I don't know if it's the fact that I don't know how I f****d up with her or something else???
Thank you everyone for reading this, means a lot!