Best friend slept with girl of my dreams, what SHOULD I do?

[T.J. Combo]

So wait, when you heard them going at it, what was your immediate response?

Did you open the door to make sure what was up?
Did you storm out of the house and leave?
Did you duck into your guest room and this post was made as this was happening?

If you actually went and laid back down and fell asleep/cried yourself to sleep, then forget about it. The time for confrontation is long past.