I read this very sad thread a few days ago and have been thinking about it on and off. I agree with what Lightplum has said, sometimes the relationship just doesn't work out no matter what.
I do wonder though from reading back over some of your posts whether part of the problem could be over stimulation? Dogs need downtime just like people and being constantly on the go can lead to the sort of problems you're experiencing, particuarly with a dog that is prone to being hyper. It could be that Sammy just needs to learn how to switch off and relax, especially if he is still a puppy. (I think your post in April said he was 9 months?) He is still growing and developing physically and mentally and getting plently of rest is very important. You have said he plays frisbee, goes running with your husband, has several trips to the park playing with other dogs and chasing crows as well as your training sessions. That sounds like way too much, even for an adult dog to cope with.
Also, have you considered his diet? It might be too 'high energy' for him and sometimes processed foods can have a negative effect on behaviour.
I don't know if you still have Sammy or are visiting the forums, so this may not help at all but if you want to have one last try then a qualified behaviourist (rather than a trainer) will be able to assess the situation and give you advice about how to improve things. But if you have really reached the end of your tether then for both your sakes it's better if he returns to the breeder.
Whatever you decide to do, you cannot continue like this:
"He has made my life a bad dream. I wake up in the morning and dread facing another day with him."