I thought my cat should have been put down a few times during his illness but the vet kept saying he was OK for a bit longer. I was getting more and more upset as he was getting slower and slower and eating less and looking skinnier all the time. One morning he couldn't get up to go to the toilet and the vet agreed that now it was time and he came over that afternoon to put him to sleep. I hope you have someone with you when it's Bruce's time to go, if it's not now then later.
I guess that vets see sick animals all the time, they know when they really are at the end, but we can't possibly imagine that they could get worse and still not be in misery.
This is how my Moo looked at the end, still makes me sad &c:ry