Who is the quote from He has lost his left arm but you have lost your right?

No, I think Lee said it himself, after Stonewall had his left arm amputated. "He has lost his left arm, but I have lost my right arm."

Stonewall died from complications of his wounds, and Lee was devastated to lose his famous partner. It seems no accident that Lee's health began to fail at this time - could have been psychological. (He wasn't on good form at Gettysburg.)