My brother started dating one of my friends a couple years back and they are engaged now. They are getting married next month and this is like a 15,000 wedding. I went by their apartment to give her some stuff and she answered in her bathrobe. My brother was at work. She seemed really nervous and I see some dude in the kitchen in his boxers. She saw that I saw. That night she called me begging me not to tell and said she has just been confused about getting married but she loves my brother and wants to get married and she will never do it again. I told her if she is sure she won't do it again I won't tell.

Well yesterday I was shopping at Walmart and I saw her with a DIFFERENT guy and they kissed.... Should I betray a friend of 9 years and ruin her wedding or betray my brother and let him marry someone who isn't faithful....