I'm so sorry to hear about Cushion. I had a cat a few years back named Samantha who had some sort of lung cancer. We knew she had a problem breathing sometimes and she had a lot of sinus problems, but one day my mom came home and found her coughing up blood in the bathroom. That's when we found out that she wasn't going to get better. It's really difficult to love an animal so much and then have them suddenly gone. I hope the both of you are coping all right. I saw your post on LJ, Cushion was a very beautiful cat who seemed happy and loved. You gave her a great chance to start again and that's what's important. Take care and take it easy.
Others have been so much more eloquent, but let me add a humble voice to the chorus: I am so sorry for your loss. Saying farewell is always hard. I wish comfort and good memories of Cushion to overwhelm thoughts of her end to both you and Adam.