I just went through this exact same thing with my kitty, Taz. Everyone told me I'd know when the time came. I'd see it in his eyes and all this. Well, he didn't tell me anything with his eyes, but at our last vet visit I had a feeling. The vet agreed and I sent him to the bridge. This was just last Thursday, so I really know how you are feeling right now. I kept wondering if it wasn't time, then I would wonder if he was in pain and I was letting him suffer. It was a horrible time for me.
So, I guess all I can say to you is when ever the time comes, please know you are doing BooBoo a favor. I have to keep telling myself that every day about Taz.

I will keep you and BooBoo in my thoughts.