I guess perhaps that dont see the relationship as unhealthy, and still believe that because there is love there the relationship should be fixable! I guess its like flogging away at a dead relationship, no matter what happens they dont know when to simply give up/walk away.

Perhaps the fact that they dont see the relationship as unhealthy, may indicate that is all they have ever known. Though they were at one stage madly in love and the relationship was exactly what they both wanted, they just want it back i guess. But unfortnately you cant undo the past, and sometimes we cant undo the pain we have caused to otehrs and vice versa.