I don't think I have any words that could bring you much comfort at a crappy time like this... I'm really sorry that the past 6 months have been so unfortunate. I can relate, somewhat, to the problem with your kitten. My boyfriend and I finally decided to adopt ourselves a kitten on Halloween 2011. She seemed really healthy at first, and then she slowly stopped eating (despite our best efforts), and we took her to the vet several times. She died on New Year's Eve. We grieved, and then got another kitten in February 2012. The new kitten also seemed quite healthy at first, but developed the typical "kennel cough" after the first couple of weeks. We gave her medicine, and tried to nurse her back to health, but we only had her for a month before she died.
I felt like I was cursed, like I could only attract despair and sickness and death into my life. I still have nightmares about the lost kittens.
I know that little story isn't very uplifting, but I just wanted to tell you that you aren't completely alone.
Kittens can be very fragile little creatures, and it's hard to get GOOD help with them sometimes. You've been doing the best you could with your little guy, and you've given him love and care that he might not have known otherwise. In no way does his sickness reflect on your abilities as a potential mother.
My heart goes out to you and your kitten.