Give me a bayonet

Ok.....this has always made me wonder and maybe someone has a better idea than I do of what the real story was. When Diestl visits the wounded Capt. Hardenburg in the hospital, he asks him in confidence for a bayonet. When Diestl seems to object, he tells him it isn't for him but the man in the bed next to him who was a watchmaker and lost his hands. Then he shows Diestl how he practiced with the other wounded man how he would plunge the bayonet into his chest. Now my question is, was that Hardenburg's original intention? Was it to put the other man out of his misery and then after getting the letter from his wife about his going into a permanant hospital gave up and used the bayonet on himself? Or did he have it planned all along to kill the other man and then himself. I wonder since he told of his plans to go into politics, like he was thinking of a future and he convinced Diestl he wasn't thinking about suicide. It does look funny though when he says goodbye to Diestl like it is the last he will see him while he is still alive. I do love this movie and saw it when it was in the theater when I was a boy of about 5.