Im very sorry about your loss. It doesnt take long to get attached to the little guys.
One thing concerned me about your post, and I apologize if I come off as being heartless. Open mouth breathing and turning down food sounds to me like it had a respiratory infection.
Everyone seems to blame this on petshops. It obviously appeared sick to you and the slightest amount of research would help you find that this was the problem. An increase in temperatures and a trip to the vet could very possibly have saved its life. Maybe this could have been a result of being in less than adequate temperatures at the pet shop, but then it seems as though it had eaten for you before so perhaps your own temperatures arent up to par.
Prehistoric pets is a "pet shop" yet they have some of the most beautiful animals Ive seen.....even Pro Exotics ran as a "pet shop" for a while. I work for one of these "pet shops" and all of our reptiles are guaranteed captive bred, healthy, feeding, given the right diet, temperatures, parasite/worm free, and if you have a problem you can bring it back and we will help you in any way we can at no charge.
Nothing is sold to anyone with inadequate enclosures, and we supply them with the number of a local reptile and exotics vet at which they can have it checked out.
When I was younger I lost some great animals due to my own ignorance. Namely, green iguanas. I dont blame that on the fact that some petshops still sell reptiles as disposable pets and gave me sick animals. I blame it on not knowing enough about the illnesses and general care for them. Respiratory infections up to their worst point I've seen cured..MBD i've seen cured...Stomatitis (mouth rot) i've seen cured....Gastroenteritis.....even fungus growing over the entire body of a cocincinus that the owner decided needed to live in water its entire life.
To wrap this up, im just tired of people treating pet shops as though they were all from the same chain and all horrible....if your mad at McDonalds...dont boycott Burger King
It hurts having people come in and tell me Im misrepresenting animals that I bred for many generations, and it hurts even more when they blame deaths on us.
When you buy a dog or cat you take it to the vet within 72 hours.....why should reptiles be any different?
Again..im very sorry for your loss..but dont get disheartened and give up...try to find out what went wrong and when your completely ready try again. There's nothing better in the world then watching your small little hatchling grow and flourish as an adult...good luck