Make a list of the questions you need answers to for Friday. Well, if she thinks she's in love w/the man, there's nothing you can do but let her go and sit on the curb w/a bag of popcorn and watch the parade go by. I'm so sorry that things are going badly for you. On another note, if they get enough of each other, the affair may just die a natural death for them.
Hang in there. I know it's scary and you are disgusted, but take it one day at a time.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.