Can I get a dissolution to save money and what do I need to do to get full custody?

I'm leaving my husband next week. He has been abusing pain pills and alcohol for most of our marriage and has recently began using heroin, I believe. He held down a nursing job until recently. I reported him and he was urine tested. Result was dilute. He refused the hair follicle test and was fired. I want full custody of our 2 boys on paper. I am willing to let him spend time with them, supervised by his parents who live next door. I spent $1300 on a divorce and canceled it.