I’ve never thought of tough love in regard to mental illness before but I guess I could see the application. But as others have mentioned it is not about “curing” anything. It means that I love you but I am no longer going to enable your behavior. You can still behave that way but I’m not help you continue to hurt yourself.

I can see how some people believe it is harsh but sometimes loving someone means you have to walk away. When you are causing more harm by enabling the behavior than good the only loving thing you can do is walk away.