You need to speak to her first. Your friendship at the end of the day is more important than a relationship that may never work out. A 'friend' recently, despite knowing my negative feelings about it, starting dating my first love and even though it ended on good terms between me and him and it was quite a while ago, her actions have still pretty much destroyed our friendship and our group of friends who share my sentiments. Please, before you decide to do ANYTHING about this guy speak to your friend about it first. Don't become like my associate, its made things very difficult not just between me and her but all of our friends have become affected too.