Hi Diva,
I just read your posts here, after writing a reply on the overanalyzing discussion. No wonder you wrote that my overanalyzing scheme doesn't work for you!!! It may not under other circumstances either, but it's certainly not going to work for you right now. You're sad, under pressure, and feeling like the spotlight is on you to make a perfect decision!
I am so sorry to read about your cat and I know you are in real pain about it. Your cat is so lucky to have had you in his life. I'm sure that he knows you love him and that you've done your best for him (don't decide to doubt that, because although I'm sure you're not perfect, you show yourself to be a loving and thoughtful person.) Animals know when they are loved. They are not like us and don't see it in a complicated way. It's you the cat is attached to and it's for good reason, you love him and show him love.
Now that you are down to making a decision concerning your cat's life and how it will end I feel so bad for you. I don't have any ideas on how to make such a decision. Only you will know what is best for you and your cat in this circumstance.
It sounds like your husband is being very supportive and I would suspect that he'd be up for a little more support, talk it over with him and rely on his strength. He's the next closest to the situation and the most likely person to be your sounding board.
I'm here if you need to vent, and I wish I had a good answer, one that would make everything better for you and your cat. (and here I am back to trying to fix what I cannot) Please know that you are in my thoughts and prayers as you go through this. Keep us posted on how you're doing.