I have similar experiences in my own life. I have been in love twice in my life, am 32 now. After the first time, I had a solitary life for like 8 years, almost complete isolation.

So when I move out in the world again, work with amazing people on a daily basis, much higher quality people than I ever interacted before, and I felt nothing and I found myself isolating myself again, there was one girl I liked. It was deeply troubling to me, again, as I couldn't figure out 'why', felt like I wasn't ready, feared the emotional damage it might do, and it didn't help she showed no romantic interest, I didn't see a path to it, and she is 12 years younger.

It was painful and it made me realize how unbalanced of a person I still am.

But then suddenly, she started to interact with me strongly, which I interpreted as flirting. It probably was flirting, but I have no idea what her idea behind it was. In fact, I believe she doesn't know either. The unsolvable nature of these puzzles trouble me deeply and make me feel there is no way to learn from mistakes.
Still, I felt like I could become a normal healthy person and I felt more masculine, but just for a little bit. I asked her out and she rejected me, stating "I have a boyfriend." and "I am not interested.". I think I scared her. I think she thought she had a fun careless interaction going on, and I made it have consequences.

I am an excentric person with odd mannerism. I am not shy, but clearly introvert and passive. I need a life partner that's extremely social and pushes me to do things.
I would never recommend her to start a relationship with a man like me. In my mind, she can do so much better.

Being friends or being colleges with her, I feel like the more mature person that likes to project himself as strong and carefree, which I am not, I feel like I for 100% cannot make an issue out of her rejection of me or my weakness in not being able to be 'just friends'.
I think she still likes to talk to me, but she may see me as someone who can only talk about science. Wether she knows how much I am into her, I can't tell. It seems she doesn't even care about knowing, which is strange.

How other people get into romantic relationships, I have no idea. More and more I am starting to believe this idea that both need to get drunk together for it to happen, as silly and childish as that always sounded to me.

For you, I think you showed a lot of weakness by blocking her or by making a big deal out of her rejection. You should have projected that it didn't bother you too much.
It should be in her brain now that she cannot be careless again with her feminene energy around you.

I guess I am glad that I can talk to her as if nothing happened, though her flirting is probably over for good as well. It seems, this is not the case with you. It has to do with the strength of both people and how strong they judge the other to be, I feel.

As for getting over her. Only one thing works. Never see her. At least, that's the only thing that works for me. You probably have much more life experience with this than I have. So you may have to decide about being hurt by unrequited love and be part of that social group, or not be part and hope it passes asap.

How do normal people do it? People know each other, then suddenly two people are close, in love, in a relationship. Then suddenly, it is over and they can just move on. Does every relationship really require one person really looking for someone that will love them back, eventhough they'd rather be with someone else, someone better? And that's how people actually get together?

Or is it just the few rare people that always fall in love with someone who has zero romantic interest in them. Wouldn't it not be much easier if falling in love is always mutual?