I'm so sorry to hear that you, like me, have been diagnosed with an invisible disabling chronic illness. I know you didn't have much say in it, but you would have done better to choose a dramatic and sudden death, maybe one of those inescapable virulent forms of cancer. People you didn't even think of as friends would flock to your hospital room and then your memorial service. This is going to be different.
I have ordered this book for you. I hope it can suggest some solution to the problem you described in your letter as "having to always have a good attitude," but more likely it will tell you how to have "a good attitude." I think that phrase is code for "Hide your pain and frustration and need, and don't look sick." Frankly, the most effective way I have found to do that is makeup, a good blush and lipstick. Anemic pallor makes people remember you are sick, and that might make them wonder whether this old age and sickness thing could happen to them. I suppose that's why they stay away.
Meanwhile, I'm so glad you have your cat. You will find he continues to value you in an uncomplicated way, even when you're no fun.