How Do I Be In Two Places At Same Time??

I don`t know what is the right thing to do with this situation: My boyfriend is best man in his brother`s wedding on 9/13/03 at 4 o clock. I`m invited to that wedding. MY problem is that I`m a bridesmaid in my friend`s wedding on 9/13/03 at 4 o clock!?! My boyfriend is invited to this wedding. Would it be proper for me to go/to be in my friend`s wedding ceremony and then depart and attend my boyfriend`s brother`s wedding reception.. That means I can make both or is it not proper since I`m part of the wedding party to leave my friend`s wedding...I need some guidance before I talk to my friend.