Okay so here is the deal. My FI and I have been together 6 1/2 years (since my sr. yr of HS). All of my BMs are my roommates from college with the exception of one girl who I met through My FI. She has been with her BF for 8 years. I have been friends with her for almost 7 years and her BF is one of our groomsman. I found out a couple months ago that she was cheating on her BF. This is not the first time and in a previous time my FI and I said something to her BF. We ended up getting blamed for wanting to break them up and her BF took her side. Whatever...no big deal sometimes someone has to be thrown under the bus. Because of our past experiences we have chosen not to say anything to her BF. Now here is where the situation changes. She is no longer just cheating on him. She is having a full fledged affair and is considering leaving her BF. She lives with her BF and her BF's parents. She doesn't pay any rent and depends on his car for transportation to and from work. Her BF has recently said to me and my FI independently that he thinks she is cheating on him. He also suspects that she has been driving his card to rendevous with the other man who is like 50 (shes in her late 20s). The word also is that her BF's mom has heard about the "affair" which means its only a matter of time before it hits the fan. I know if he finds out the extent of the cheating that things are going to get really really ugly. She is my friend because her BF is one of my FI's best friends. Although I consider her a friend. Her BF is much more important to my FI that she is to me. I had never even considered having to kick out a member of the WP but my FI does not think there is a choice. He doesn't want me to give her any info about the BM dresses because he doesn't want this all blowing up and us having to ask her to step down. I just don't know how to handle this. My 5 other BMs are my college roomies and they all talk on a weekly basis. The cheater is already kind of the the odd girl out but my roomies all know her and do their best to include her. I would love to hear everyone's advice on this situation. I personally don't want to boot her but I also want our wedding day to be about my FI and I, not her and her BF having a screamfest.