It’s painful to see someone you like, liking someone else, but it happens. Does your friend know you like him? If they both like each other, can’t you try to be happy for them? I know that’s not easy, but you can’t change facts. All you can do is accept it and try to be happy for them. Just like someday your friend will be happy for you when you like someone who likes you back. That day will come, even when you don’t think so right now.