How can you convince a guy isnt right for her?

a friend ive known for 4 years now has this boy friend who at one min. seems like his old caring self around her. can change to a total diffrent person who treats her like she isnt woth even pocket lint. ive mintioned this to her and she countines saying their is some thing that she has to figure out first. (which confuses me cuz she wont tell me what). or some thing like we have a long past together which i understand she was pregnant for a while with his child but she became stressed by him and doctors said stree was what made her loose it. im not sure if this has any thing to do with while she staying with him i do know that he is always making her sterssed out about every thing