White knights can rarely win if the girl is mentally imbalanced, dsyfunctional or plain needy. Been there, done that and my brother is now paying for it in his marraige. My brother, who is a therapist thought he could rescue this girl that adored him and now that they are married despises him.
People who have their act together can solve their own problems. Stay for the short term but dont get sucked in other than appear concerned. If there is something that can be solved quickly, help, otherwise observe and commiserate.