Hmmm ... strange situation, I must say. Ofcourse friendship is more important than poker, but I would never let a friend win just because he can get upset if he looses. If the both of you are good friend, you should be able to talk about it afterwards no? And if he knows enough about poker, he should know that it had nothing to do with you, but with the chances and luck. And IMO friendships can go through rough times, but normally both of the friends learn from it and become even better friends when you survived the storm. I would be more upset when I found out the friend let me win in a game.