Who should be responsible to pay the BILLS???

I am a mother of 4kids 2 of which is my boyfriends that I have lived with for 12yrs. Our children our 10 & 6. My 2 our 18 & 17 and almost out of the house. I have been taking care of the older 2 on my own for years and have not asked him to help. I work part-time overnights and have for the past 5yrs to be at home with our children so we have had no daycare exspence. He is self employeed and works long days and many into the late evenings. He has started to ask me to pay some of the bills. Keep in mind I buy most all of the food, paper products, cook, clean inside and out. He only pays the Bills. I use the car to do things for our children, but I also put gas in it. He has resently refused to pay the gas bill and our gas has been turned off. He has said I can pay this if I want it back on. He is not hurting me by leaving the gas off he is only hurting our children.