ㄹ 만큼 하다

I've done all I can

Repeating 하다 around -ㄹ 만큼 says you have done as much as there was to do. Every line here is a form of 할 만큼 했다, and it is used to close something off: 형은 할 만큼 했어, 이제 포기해 'you've done enough, let it go now', 서로 이제 할 만큼 했다 of a relationship that has run out of road. The tone is settled, sometimes worn down, not proud.