When to Say Goodbye

I am struggling with deciding if it is time to say goodbye to my almost 20 year old boy. How did you know it was time to say goodbye? He hasn’t been diagnosed with a terminal illness, but he’s becoming incontinent when he sleeps, cannot keep himself clean, doesn’t move much, and having mobility troubles with his back legs. He’s on multiple meds for arthritis. I’ve tried diapers, and potty pads. The problem is he has long hair and so the diaper either soaks his hair or he walks through the wet potty pads. I clean him up the best I can’t, but full baths are too much for him. He is still eating and still perks up when he looks at me and wants to snuggle. Everyone is telling me it’s time, but how do I look into his eyes and kill him? That’s what I feel like I will be doing if we put him down. He is the most emotionally intelligent cat I have ever had and the only cat I have that snuggles. He has never once tried to bite or nipped at anyone, even when getting a bath or sanitary trim. He is the most easygoing sweet boy. I feel like I know I need to and let him go with some dignity, but I’ve never had to do this as an adult before, being that it is my decision. Please any advice or experience to help would be great. Thank you!

Update: thank you all for the kind words. We took him to the vet this morning, this vet has known him for several years. She said the kindest thing was to let him go, that it was definitely time. My heart is completely shattered. I just wanted more time with him, but I know he was hurting. The hardest part was mentally he was still engaged and wanting to snuggle, the sweet look in his eyes, but physically he could hardly move. I love him so much. I just hope there is a heaven and that he is up there laying in the sunshine now ☀️🐈‍⬛