Thank you so much for all your lovely words, I set myself off again last night, couldn't see by the time i'd finished, sorry to ramble on but I had to let it out, and reading your lovely replies has set me off again. Can't let him see me like this, he's struggled as well.
We have talked about going back for another but somehow this time I just can't, not yet, we have usually had 2 dogs at a time, most middle aged when we got them, so we've seen a few come an go, but none were as special as Jack, and it seems wrong to think we can just go and replace him.
I remember the picture in the hayfield so well, we'd had him about 12 months and he's settled down and looked so relaxed and happy.
I think Colliewoman? says somewhere there is a group who get the 'free to good home' dogs (collies?) off the adverts, maybe when we are ready I'll find out who they are.