I have recently posted about a very similar problem to yours. When we got a new pup (not a cocker, a Vizsla) Charlie kept running off. It was very scary and very out of character. He just stopped listening and got really hyped up, he wasnt bothered with any of his treats. For a while I walked them separately and spent some time doing some less exciting walks with him in areas I know he doesnt get so distracted, I have an overflow campsite field me which the owner gives us permission to use in the winter. This gave Charlie a chance to calm down, spend some time with me, so I could go back to basics with recall using the pups very long line. This really helped and I started to walk them together again. However, Charlie then started barking at me a lot on our walks and constantly which only stopped when I put him on the long line, each time starting again when I took it off, so he is walking at the moment quite happily on the very long line, usually trailing and if I am near areas I know he could run off I can pick it up. But for some reason it has really relaxed him. Its very hard to understand sometimes... I hope you can work something out with yours soon. I am sure you will be able to enjoy your walks again soon.