aww Carrie, this must be pretty stressful for you :/
I'm kinda of the opinion that you can be happy wherever you are if you're happy with yourself.
If you're not content with yourself then you start to look around you and pick at things, it sounds like your Hubby didn't feel like he fit in in the US, but doesn't feel like he fits in in the UK and that can be a daunting and scary prospect which probably left him pretty confused and angry.
He probably put it all down to not being in the UK ("at home") and now he is, he still feels the way he did before and so is blaming the UK for it, has he thought that maybe he doesn't feel like he has the things he wants of needs to feel comfortable and sucessful and so lashes out at his surroundings?
I'm not at all saying that he isn't a success or anything, but sometimes, in people's heads they can get funny ideas that they "should be" more successful, earn more money etc, and even though that's crazy, they're fine just as they are, those feelings of inadequacy can creep in and make them unhappy.
Maybe you guys need to sit down and talk about what things need to change in order to make him happier and more at ease in the UK, maybe it's a case of all his friends have moved away whilst he was living in the US (4 years is a long time) and he needs to reconnect with them, or to make some new friends.
If he hates the lack of community, maybe he could join/start a neighbour hood watch scheme, or have a BBQ (weather permitting!!!) and invite some of your neighbours.
If you did decide to move back to the US and he's still in this state of mind, you might find he'll just start to feel the same way as he does about the UK. Nowhere is perfect, especially if you go out looking for faults because something internal is driving you to.
The grass is always greener if you choose to compare the two. But if you just look at what you have, and try to make the best of it, he might end up happier.
I don't know if all that made sense, I hope it does.
take care x