Antonia, I'm sorry that you are losing your kitty. My H and I put our Lab down last year, together. It's always hard.
I agree with beatrice and seeking (as usual). I would tell your XH, just the facts. If he wants to be involved, he will; if not, fine, but at least he won't resent you for not giving him the chance.
I have a vet in the family, and can tell you that they receive a lot of training in the bond between people and their animals, and how hard it is on most of us to lose them. In both of the euthanasias we had to do, the vet and techs were very, very tactful and understanding, and, in fact, cried with us. Don't be afraid to lose it. And try to get all of the paperwork done before you see the vet, because you will likely not want to hang around for it later.
I'll be thinking of you tomorrow. And I'm so sorry!
M 65 H 64 T 39 & M 36 @ S 12/08 Two Ds
Do you know that the harder thing to do and the right thing to do are usually the same thing? Nothing that has meaning is easy. ~ The Weather Man