I was in a similar situation several months back. My mate was extremely ill and I was too far away to see him. It was tearing me apart. I felt so horrible because I couldn't do anything to help him. But as much as it hurts, it's best to try to let go of things you can't control. If you let the worry eat at you, it only hurts yourself. I'm sure your friend understands that there isn't much you can do and greatly appreciates you showing how much your care through text, just as my mate did. Just keep doing what you can; that's what matters. My mate was lucky enough to fight through and is in much better standing now. I'm sure your friend will be able to make it through his struggles as well.