I need a reality check. Sorry for the long story.

I met a girl a few years ago when we were both in high school and about 14-15 years old. She went to a different school in a city about 20 mins away from me but I happened to be the first person she talked to when she visited my town with her friend. They were looking for a spot to smoke some weed so I happily obliged and took them with me to my usual spot. Keep in mind, this was completely new to me as at the time i had absolutely no confidence, and the idea of telling a girl how I felt about them was completely alien, which remains true to this day even as a 20 year old. Everything went well despite my overwhelming nerves, and I got along with both of them, adding them both on Snapchat when they left in hopes I could see them again.

A few weeks passed and we made plans to see each other again, but this time only one of them was going to come, and she wanted to go to a carnival with me. This is when I started really falling for her. We went on a bunch of rides together and had a great time, but I was so nervous to finally be in her company i came across as if I didn't want to be around her. I ended up seeing some of my friends there and we went somewhere away from the carnival all together to go hang out and smoke. I still regret it to this day but I sat at a completely different table and barely gave her any attention. She asked us if anyone wanted to come to the store with her and I didn't even respond.

When everyone left my friends told me she was sitting there waiting for me to come sit with her and wanted to go to the store with me. I somehow convinced myself she didn't want to be there with me and they were just trying to make me feel better about it, but looking back on it makes me feel evil and I get a paralyzing flood of regret for how I completely ignored her and pretended I had no opportunity to spend time with her. That was the last time I saw her and I immediately felt a shift in our communication afterwards. It's been like that since and I mostly forgot about it but I had a dream last night where none of that happened and it was very intimate (nothing inherently super sexual, but it did involve caressing/skin to skin near the end) basically i guess it was just some sort of "day in the life" of what could have been if I wasn't so terrified of telling her how I felt.

I haven't stopped thinking about the dream and it brought back all the feelings I had before but it's so much harder to deal with now that I know she has a boyfriend and I'm still hung up on something from like 4 years ago. At this point I know i can't have her, and I don't want to waste time trying to change that. I do however still feel awful about how I treated her and Im stuck trying to figure out if it's worth apologizing or if I should just leave it alone. I also need to be told if this is pathetic or if this is justified, do I need to just man up and stop thinking about what could have been? It's just so hard when I can't even begin to compare anyone to her. Im lost guys

Tldr; had a dream that reminded me of a girl that I couldn't confess my feelings to, and Im losing my mind trying to navigate these feelings again now that I recognize what I could have done, but I can't do anything now that she's happy with someone else. How do I (or should I even) communicate that it wasn't her fault i didn't reciprocate her attempts to be around me? And is that even possible without completely ruining whatever's left of our friendship Im desperately holding on to?