Three weeks is still raw just purely based on the strong polarising feelings you're experiencing. Getting over the feelings now might seem confusing and difficult, but you've clung on to one good thing with clarity and that's that you don't want her gone from youe life entirely because she's a good person. It's good that you can already see the patterns happening on loop. It might be worthwhile to outright draw the line and let her know these medium-term goals you have (remain as friends/good friends), and that right now you might need a couple of months to focus on the present and cool down - and during this time she may not hear from you but it does not mean that you are cutting her out entirely.
I'm reading that you might have a strong need for control, you want the goodness she brings (which seems to be unique to her that nobody else provides). Your feelings of anger might be because her decision to break up effectively cuts you off from the goodness she brings. She has her own life and maybe even her own issues; whatever it is, it's led her to conclude at this time that being in a relationship isn't right. Respecting that will make you stronger and more whole as a person.
Try to take it as a valuable life lesson.
I'm not sure if this is the same, but when I was young I dated a good friend and when she broke it off it was rough. We had a lot of fun together, lots of jokes, banter and inuendo during group outtings, so it made sense to progress the relationship. But it didn't work out as I was too immature at the time. It took a really long time to get over her, love myself again, and accept that I did not exclusive rights to her. Utlimately, years later, I found out that she had her own issues too. By then, I didn't think "it would've been great to know it sooner so I could get over the grief faster". I didn't think "I could have done more and been a better partner for her" either. I accepted what's done was done, and let the moment pass.
