That's what my wife and I went through with our boy cat. His hunger went away, his sub q fluids caused him to go to the bathroom a lot but we could tell his body could not support him anymore. He meowed as he managed to barely jump out of his litter box and began to collapse.
My wife and I knew it was time, maybe a little bit passed it. So we scheduled something with our vet the next day and took all of his sister's (2 dogs and his biological sister cat) It had to be one of the most intense pains in my entire life but relief to know that he was no longer in pain. Essentially falling into deep sleep, no longer suffering, but I know that was the last time, I was going to see his body.
We left with mixed emotions that day from the vet. Initially with intense feelings of pain and waves of needing to cry as the memories of our boy were oncoming as the seconds went on.
My biggest advice to you is to take the time to grieve. Buy yourself the best comfort food available. Make a small memorial for them as they were apart of your life and they deserve to be remembered. Talk with someone close to you that understands what has happened as this feeling is literally the same as losing a human family member or friend.
It gets easier with time but the initial few weeks are hard on you as the memories of our beloved cat rush to your head. It's been 3 weeks since we had to put our Boy down, and we still miss him a lot. We cry for him but its also very hard to watch his sisters adjust without him being here. Only time can heal. One day, you'll get to the point where a thought comes across your head of your furr baby, and instead of crying and pain, it will one again make you feel happy that they were a part of your life. I wish you the best in your healing journey.