Why is everyone saying he died because of the source!!!!!!!
Why the hell would they show him get stabbed, and then hold his knife wound to his death if he was in so much pain from the source! He didn't show any pain after the source!! If it was the source that killed him, he would have died there and then.
We all saw how much pain Desmond was in when he got blasted by the EM, did Jack roll and scream in agony? No. He just walked slowly, holding his wound. Lowered himself down, still holding the wound, showing no signs of the EM.