Calloway is one handsome guy! He looks very huggable.
I'm sorry that he has been diagnosed with diabetes. Moesha's post sounds really hopeful and maybe diet will be enough to lower his blood sugar. Do you think the litter dust might be contributing to his asthma? I always wonder about that with Jim. Prednisilone is supposed to be helpful for asthma and thankfully is cheap. At one time I got a puffer for him that the vet prescribed and a baby chamber thing to dispense it to him. They make ones for cats but they are more expensive. I stopped using it though because he got kind of freaked out by the chamber thing.
I hope he starts feeling better soon and that he likes his new diet.