Have you asked about DBT?

Optimal frustration is when the therapist isn't able to meet some need that you have. The idea is that when the therapist isn't there to meet the need then the person finds themself meeting their own need. That results in strengthening of the ego / self.

But that didn't happen. Because (as you said) you aren't able to deal with frustrations. But I guess he is going to have to figure something out. Because he isn't perfect. Because he will burn out if every time he is imperfect you go on to hurt yourself. So I guess it is back to figuring out self soothing and emotion regulation and alternatives to self harm.

That is why I suggested DBT. Skills skills skills...