How can I help an Alcoholic?

My boyfriend has had 4 D.U.I's and his parents have spent thousands of dollars on lawyer's to just keep him out of jail. He refuses to go back to rehab. He only has a restricted license to drive back and forth to work but he still drinks and drives If he gots a 5th D.U.I, I am leaving him but his parents want me to stay with him and try to work it out. We have a daughter together and he still drinks constantly! How can I help him!