I can understand, even though I have never had kids. In time things will get better and it sounds like your situation is not fair. Your kids will grow up and after that you won't have to pay support anymore. Well I will be honest with you because if one isn't honest one can't better themselves, and it may sound harsh, but sometimes its kind to tell it like it is. You are tied down right now with a ball and chain. Maybe this is a time for you to find happiness in small things in life or if you have a talent in a hobby you can find a way to earn extra income. Try a 800 number for men to earn extra money, one of the sex numbers. You can work when you want.
Your not the only one or the first one to be in this situation. I worked with this guy once and he was like you, almost his entire check went for child support. His wife lived in a nice house and remarried and her husband made a lot of money and she started working and made a lot of money too. He wasn't able to get his support lowered and he was almost living in his car and his x-wife was eating steak and had it all. Well I didn't want to depress you, but like I said, I would rather tell you the truth like it is.