Sometimes the best form of mediation is taking a step back and letting the disagreeing parties duke it out for themselves. This is the approach you should take today. Even though you really want to make things right, and even though you may really care about the outcome of the situation and the people involved, your interference today might just make things work. Take yourself out of the equation. Tell them they need to handle the problem themselves and that you won’t be the middle man anymore. What happens after that is up to them, not you. Even if things get heated, it will work itself out and the fighting friends will get some stuff off of their chests that they might not have been able to say to you. So leave them to it.