HI I've not posted on here in a while but have been reading your story and feel for you. No one can really give you advice, but I think you already know what will do. It just takes a while to get there.
I just wanted to say I agree entirely with Joules. By hook or by crook get yourself and Archie to Cornwall asap. I'm only posting because we've been in a similar situation. We had a wee cocker called Mollie that we "managed" for 5 years, but we'd both been bitten before we figured out how to deal with her. She was more my OH's dog. Anyway she just seemed to become more and more unhappy as the years went by, and it sounds as if Archie is one deeply unhappy dog. It would have gotten worse as we've had 5 grandchildren born in the 4 years since she's been gone and obviously we want them to visit. What did it for me was that, while we could manage her, her behaviour towards our other dog, Alfie, just got worse and worse, to the point where he was terrified of her. We had a darned good behaviourist, David Ryan, come in and got lots of advice and training to do but honestly, it didn't avail much.
I thought perhaps she might do better as an only dog and, finally, OH agreed to her going into the rescue where I volunteer, under assessment with a view to rehoming. I knew in my heart she would fail the assessment, and she failed spectacularly, and was deemed unsafe to rehome. I picked her up from there after her week's trial, took her to the vet and had her put to sleep. It hurt badly because she was so overjoyed to see me because she thought she was going home, and I took her off and euthanised her. At least she died in my arms (with a muzzle on!)
I don't regret it, even though I learned later that there are some outfits that will take dodgy cockers. It was the right thing for us, as I do believe that there are worse things than death for some dogs, and at least I know what happened to her. I moved on pretty quickly but OH was upset about it for months.
I'm not advising what you should do. I just wanted to tell of my experience. Mollie was 6 when she was PTS, and I just couldnt face another 7 years of life with her. For me, I just think there are too many lovely lovely dogs in the world needing a home. This for me is why I would never buy a pup. With an adult rescue, I know exactly what I am getting. You never know how a pup will turn out.
So good luck with whatever you do. Only you can decide. Wishing you all the best.
Diane xxx