How do I divorce after four years of separation?

My wife left me in South Carolina and took our two children to New York. It has been three and a half years. She has been with another man and I want a divorce. I cannot afford and pay child support at the same time. She makes more money than I do as a single man lost his income. My wife and children just want to move on. What do I need to pay in child support? I think I pay too much, $240 a week average and I average $750 before taxes. She takes advantage of me.