Well do you have any idea of what kind of tree it is? Tell me if the black pebbles are glued down or not (if they are, pry them up starting from the edge of the moss so it all comes up in a layer of chunks). You haven't said if your tree's living outside or not, how much sun it gets for how long each day, how often you watered, by what method and how much you give it, etc. etc. With no info at all, it's a little hard to help. I will guess that's it's a chinese elm (Ulmus parvifolia) for now though, and tell you that trees with no leaves need to be watered infrequently, but that when you do it, do it well enough so it comes out the drain hole. However you can't judge when how much of the soil is dry or not because of the pebbles, so get rid of them first and provide more info here.

wow I'm sorry I left out important information like that. That was really silly of me.

Well it is a spring azalea bonsai. I leave it outside in a place that doesn't get direct sunlight on it a lot, but still a little bit. I water it using a little measuring jug, giving it enough for the soil to get wet and the water come out the drain hole at the bottom. It has been raining the past few days though so it has been getting a lot of water. There are no pebbles on it, i'm sorry if the picture makes it look like that. It's only soil in the pot. I thought perhaps repotting it may do something, so I put it in this "self-watering" pot (I think it just works through evaporation of the water than comes out of the drain hole).

Hope this information helps to help me!
Tell me what I've been doing wrong.

Oh, in case you're wondering, the things that look like "pebbles" are little pieces of bark.
This pot I'm using now (I only repotted 2 days ago) it's much bigger than the one I got with the bonsai, and there is little of the original soil in this pot. Should I get a different potting mix for the bonsai? I'm just using a general use soil I got a while ago to fill the rest of the pot.
I put the general soil at the bottom of the pot, but towards the surface, closer to the bonsai I put its original soil.

First of all, don't layer the mix at all, no matter what it is, no matter what tree it is. It should be mixed completely. Second, you'll see that when bonsai people talk about what they grow, they refer to them as trees, and/or whatever species they are, not as 'the bonsai', which half the time the trees are not (yet) anyhow, and which does not help to ID them either. Azaleas are one tree that need tons of acid in the mix, so if they're not in almost pure peat (how they're generally sold) big doses of acid fert. are needed, and it's mostly easier to leave them in the peaty soil they did come in, plus the usual problems of slow drainage (in that mix) won't apply as they also love lots of water... in fact the danger comes when the peat is allowed to dry out, and then it's hell to wet it again. Ditch the moss, it is fighting the tree for water. Snapping off branches BTW, is not the way to do things, and the season is wrong anyhow. There are special bonsai tools for cutting branches properly - in the right season only though, otherwise the tree will be very stressed. If your tree is going to recover, it will do so when it feels like it, but I have to say that it sounds like it's too late. Don't feel bad - store bought azaleas (unless they really are proper bonsai sold by bonsai dealers) are tweaked to bloom out of season (very early spring) which makes them difficult to use for bonsai. If you want to grow bonsai, then start doing a lot of reading (before spending!) and find a local club to join and find out what everything's about, but don't just go buying trees before you know if they're suitable for your environment (in or out) and if you have the skills and knowledge to grow them.