Wow, I am really sorry you have had to go through all of this. I have heard bad stories about fostering both skinkids AND furkids. It is sad because the foster parents are largely loving and compassionate people and there is so little to gain from it and so much to lose:( Then, the best foster parents end up quitting because of things like this.
((((HUGS)))) to you for your sadness at losing this sweet kitty. I hope you can let yourself have the time you need to grieve because you need that.