You don't need to feel sorry for him and you also don't need to punish him.
The solution might be to encourage and support him to save himself. That doesn't mean doing things for him, but it might mean encouraging him in things like therapy or finding out what his "small steps" might be towards his goals (and sharing yours with him, he might be motivated to figure out how to support you in your own goals and dreams).
When he does something good, succeeds in a small step, offer positive words, "That's great, I'm happy you succeeded in that step." If he is down, listen and validate, but don't coddle. And if he has a misstep, do your best to not bring it up to him. He's likely expecting that, so give him something different. Then, he can't react and behave the same way he always does.
