It's your depression talking and telling you things will never improve. Depression lies. The only thing constant is change, and you will not feel this bad forever. When I'm depressed I can feel hopeless and like everything is painful and meaningless, and it feels like it has always felt that way and will always feel that way. But then I come out of it and realize how narrow my thinking had become, stuck on the same thoughts and feelings, just repeating and gnawing at myself. But it is always temporary, and things do get better. Things will improve for you too, if you can just hang in there through this crisis. Hospital is there as an option if you can't keep yourself safe. There are reasons to live, but maybe it's just not possible for you to see them right now because the depression is blinding you.

Also, I'm really sorry to hear about your cat. Try not to take it personally. You don't know why he hasn't come home. I'm sure he loves you very much, and I hope he is OK.