Theresa, I'm so sorry about your friend. Several years ago we lost a very good friend to cancer at age 50. There really was something about losing someone at that point in their life to such a senseless disease. And what a helpless feeling.

I don't know if there is anyway to feel ok in this situation but I do know you should try to not beat yourself up(easy to say, hard to do---I know).
You are only one person with a certain amount of resources. And I would bet your friend would tell you that you are doing exactly what you can do to get through this.