Hi, need some thoughts. Dtr. with wrong guy, what can/should one do?

this guy is a total loser, drinks, poss. drugs, lazy, dropped out of college, diagnosesd with paranoid schizophrenia, mean. over 6+yrs has made her cry and be sad many times. he has broken it off several times but she begs him to come back. She seems to not be able to let go. He is no longer welcome in our house but I know they see each other still ocionally. She secretly still calls him everyday. She will soon have a well paying job and NOW he's interested, even though he keeps her with a minimum of involvement on his part. I am afraid he is going to riun her life if not worst. as it is he is never there for her and will undoubtly never will be. When he was welcome in our house she sat alone most sat & fri. because he would go out with friends, still going on and not new since we told her we don't approve of him after holding our tongue a long time. Is there anyway to help her see the light or must we watch the tragedy happen! Needs to like herself enought to let him go