I am a guy with a female best friend as well. I've known her since college and she is the the I go to talk to after my wife, who she also has a great friendship with. Unfortunately, I don't think what you guys did was an accident. If both of you were willing to go through with this, there were underlying feelings on both sides. I love my best friend second only to my wife but I would never do anything sexual with her. I know she feels the same way. You should pursue a relationship with your friend and if that doesn't work out, that's life.