Hi CM I just picked up this thread and read it through to the end. Your situation reminds me somewhat of my own situation just over a year ago.
I live in Swindon (well someone has to, lol), but DH works in London, so obviously it's a bit of a commute for him. He got fed up of the commuting and decided that we should move to Surrey to be closer to London. I wasn't sure as I am settled here, and I don't make friends very easily, but DH convinced me that it was the right thing to do. We sold the house and everything, found a house in West Byfleet in Surrey, and were within about a week of exchange of contracts. As the process continued I became more and more unhappy, until eventually I got to the point where I just didn't see myself staying with him any more (we have been together for 10 years). Then one night it just all came to a head when he realized just how much I had backed away from him, we had a very long conversation, and the outcome was that we're still in Swindon. He never realized just how bad things were for me, but all I could see was that he would have his friends that he currently has, his same job, the same people, whereas I would be in a strange place with a 2 year old. The reality was that DH was absolutely mortified that I was so unhappy and that he felt he was the cause, he never knew it was that bad.
There are two people in a relationship, and your DH needs to realize this, if you left, (and I am by no means suggesting that you should even consider doing that), but if you did, the likelyhood is that the children would go with you as you have been their main carer for the first years of their lives, and custody normally goes to the mother anyway. But it's worth using that as a trump card if ever you have to. good luck