Kumquat suddenly dropping leaves

Ludwik1526 starts with ...
Hello

Recently my kumquat has been dropping leaves - a lot of them. I am struggling to understand what is wrong and how I should act to save it. Around 1.5-2 weeks ago there was a ton of flowers, most of which seemed to be pollinated at the end. And everything was fine until suddenly it started dropping those, after 2-3 days there was nothing left of the new fruitlets... And I thought that maybe it's just decided that it's too much given that there already are fruits ripening but then in the last days also more and more leaves have been falling - every day it gets even worse. If this continues, very soon it'll have lost around half... Some of them are brown-ish, some seem to be completely fine.

About the conditions it had, since october until recently it's been standing on a window sill and watered regurarly, mostly around every 2 days (every second time with biohumus), as it seemed to be the best interval for it and worked just fine. For the last 3-4 weeks I've been taking it outside during the day, as the temparatures were around 20-25 degrees celcius (68-77F). Oh, and every time when I watered it, I was also spraying leaves with water. And that's pretty much how it was. For the last 4 days I haven't watered it and I didn't move it outside, as I first thought that the most probable cause would be overwatering (somehow) but now I am beginning to doubt that this is the reason. I am quite sure that it's also not any insects, as there is nothing to be found. And I already dealt with spider mites so surely not them this time.
I am seriously scared that it's not gonna make it so any advice or suggestion will be highly appreciated. Below I attach some photos.

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