One thing Dylan keep the tree outside no matter what. Sounds like an iron defiency, but if the foliage is spikey and when touched falls off then most likely its gone
Also does the bark looked shriveled if so its probaly dehydrated, but its too late. But if it is not spikey and the leaves just yellow turn brown then fall off then its probaly an iron defiency. If so get some chelated iron from your local garden center,or bonsai nursery.
