My old dog (not a cocker) suffered from dementia in the latter stages of his life
It is such a sad think to see, when you look back and remember how they used to be. He lived to 2 weeks shy of his 15th birthday, but in all honesty the last 6 months of his life were more for me than anything else as I just couldn't make the decision
He would look blankly at me when I spoke to him as if he didn't recognise me, he couldn't hear me when I called him and he used to just stand in the middle of the room for ages and just look at the floor as if he didn't have a clue were he was. He also started to do the toilet in the house and I honestly believe he didn't even know he was doing it
I can only sympathise with your dilema and only you can make the ultimate decision which I know and many others will to, is the hardest on of all to make. You really have to be at peace in your mind about this. I hung on for as long as I could (for myself), maybe to long, in the end I had to think about his quality of life and not about my own selfish reasons. I remember him today as my baby and my dog of a lifetime, I have a picture of him beside my bed and don't regret my decision although it was extremely difficult.
Thinking of you.