Tell him of specific, concrete ways in which having him around improves your life. Remind him of specific, concrete shared history that made you happy - advice, jokes, shared adventures, etc. Tell him of your hopes for a shared future. Let him know how much you value his being here.

Must be terse as I am sitting in company meeting.
Recent research indicates that suicidal thoughts are caused by only two main factors:
1. Being inured to human suffering - as in this case with chronic health problems.
2. Loss of emotional support network.

You can improve the second, although it will be hard to do from so far away.