I'm so sorry for your loss
I so know the feeling, a couple of years ago, we had a Bombay named Jake, one day he just let out a yowl and collapsed on the floor, we took him to the vet and they said he had a blood clot at the fork of his legs, he still had some circulation in his legs, he would pull himself along by his front paws, a couple of days later we noticed one of his legs was really cold, so we took him back to the vet, they said he had lost the circulation in it, they gave us the option of amputating or uthanizing, we chose amputation.
He did really well at the vets and at home, his wound was healing well, about a week and a half after he came home we noticed the other was cold, this time the vet said it would be too cruel to amputate the other leg. It was the hardest thing we ever had to do, we bawled for a long time, still do when we think of him. He had the most wonderful personality, love to talk and be hugged, he has a twin brother (sunShadow), while Jake was sick sunShadow never left his side, it was amazing, they were actually talking to each other. When Jake died, sunShadow would let out these long mournful sounds, it was so heart wrenching to hear, he did this for about a month. Our other two cats at the time didn't really do much, the odd time they looked like they were searching for something and meowing. But being his twin, it hit sunShadow the most. The interesting thing is that before he wasn't as cuddly as Jake, however after he just can't get enough of us, everyday when I'm sitting in my lounge chair, he comes and curls up on me.
I have to agree with hissy about keeping cats indoor, When jake and sunShadow were about 1 1/2 years old, sunShadow used to love going outside (Jake didn't), one night we heard a meow at the bedroom window, we always left it open so they could come in and out, we looked out and saw him (sunShadow) at the base, he wouldn't jump up like usual, when we brought him in we noticed he was limping a little, but otherwise unscratched, this was on a saturday morming aroung 2a.m.. Seeing as there wasn't anything visible, other than a small limp, he seemed okay otherwise, we decided to keep an eye on him until monday morning when the vet was open. Monday comes along and he wasn't improving any so we took him to the vets, they told us that he apparently had been hit by a vehicle because of the way his claws were broken, they did an x-ray and discovered that he had a cracked pelvic bone and was bleeding internally, he had a very severe infection due to it, we, of course felt like the worst parents in the world for not taking him immediately, he spent a week in the hospital and $1200 later, we decided that they would no longer go outside. There are so many crazy drivers out there, and being a black cat, it's hard to see him.
Please except my condolences to you and mikey's twin and hugs to you both