Hey, sorry to hear about this situation. It sounds like you're being supportive, so that ought to be a huge help to him. Other causes of ED can be hormonal (I've heard that oral medication for hair loss can have ED side effects, for example), also arterial blockages (not just from diet and that, but it could be from injury where the blockages would be localized), also scar tissue... I'm not sure if he has taken Viagra or Cialis but that could be a help. There are other more invasive interventions available now too that he could try, depending on the cause of the issue.