That's some heavy stuff matey, and I'm no shrink, but the one constant is you must be happy with yourself before you can make others happy around you. Theirs no point kidding yourself, making others happy at the cost of your sanity is ok at the start, but it eventually catches up and makes things even worse. Although I'm not in a complicated situation like you, with a family, I decided to change my life in a big way, very soon - because I was doing my job to make others happy, not myself. I got depressed and was bitter, then I remembered I used to be a much nicer person - so I made the jump and I've felt better ever since.
I sometimes think of people who have it MUCH worse off, and it gives me a moment of reflection, but to be fair it's not enough in the long run, if there's anything you can do to make yourself happier you should do it.
Parents that I've spoken with, say that their job is vitally important in their family, not just financially, but as an escape, everyone needs time to themselves away from the responsibilities of being a parent and a husband. Have a night dedicated every week for "friends", go out bowling or to the cinema with friends, without the wife and kids. Balance is the key in any successful relationship.