So I'm new to bonsai trees and after having this (what I assume is a) Japanese maple for around 2-3 months, its leaves have starting yellowing and withering, I have had issues with it since the start but I have managed to solve them by repotting getting a simple fertilizer, but now I feel uneasy about doing anything just because of its state, could it be that I'm overwatering it or keeping it too close to the cold, seeing as I live in Sweden and our weather isn't the nicest, especially as I have open windows.

For some reason the leaves are only withering on one side of the tree, the other ones are still kinda healthy.

uhm.. It is fall turning to winter.
Your tree should not have any leaves at all at the moment. Be careful now, if frost starts your tree is very sensitive to it as long as it has not dropped the leaves.

Why does it still have leaves? Do you keep it in a very warm spot?
Please tell me you do not keep this inside..

((I might have double sent or messed up, my wifi went down when i first tried sending this jhbds, man im stupid))

I haven't considered looking up info about it losing leaves so I didn't consider that option, apologize for my stupidity.
And sadly I keep it inside due to living on the fourth floor of an apartment and the neighbors here are quite fond of stealing whatever they can get their hands on, so I can't have it in the pots outside, as well as not knowing that it had to be outside, so that's my own fault, but if it's a must, I would love some advice on if it's allowed to still be in its pot while hanging from a window or something like that.
I feel stupid over how much I have hurt it now and really would like help on what to do with it twt