I cried when I found out my sweet little furball was diabetic. Now about four years later, she’s 15 years old, still happy and sweet as ever. In fact, she’s snoozing happily against my leg right now. I give her two injections a day, I’ve been able to find cat sitters who can (or can learn) how to give injections, and in general she’s doing great.
You’ll be fine and your kitty is more than capable of having a long and happy life beyond the diagnosis.
A bottle of insulin is about $130 but lasts ages, and I’ve had her on Hill’s Science Diet m/d glucose management food for years even before she was diabetic. My other cat had kidney issues and the easiest thing was to feed them both the m/d, particularly because the vet said it’s basically one of the best things a cat could be eating anyway since they’re obligate carnivores.