NEEED ADVICE NOW!

Okay, so my best friend of 4 years has been in a relationship with this guy for a little over a year now and is really unhappy. I was trying to give her advice and I told her she needs to do what is right for her because life is short. Well, let's just say she got really emotional and then she said she had to tell me something but I had to promise I'd still be her best friend no matter what. I promised, of course because I couldn't think of anything that could break up our friendship, she's like a sister to me. Well.... She told me that ever since we met she's been in love with me (FOR FOUR YEARS). I'm not attracted to women whatsoever and I'm in a long term relationship (I have a fiancé and I love him to death). I didn't get angry or upset because I support people finding their sexuality and being proud of it. But she's in love with me, I told her I'd still be her best friend, that its not a serious issue because you can't help who you fall in love with, but I also told her I never felt the same and I wish I could have saved her from the heartbreak of falling in love with me because we can't be together romantically. But I told her that nothing between her and I will change (which I'm hoping it won't because she's my best friend and I don't want anything to change). But here's where it gets messy. She's dating that guy who I talked about previously and she's planning on telling him Wednesday August 10th that she's in love with me and has been. So my problem is 1) I don't know how to deal with this information because I was in such shock and 2) I work with her current boyfriend (that will probably soon be her ex boyfriend) and I don't know how to stray away from drama within the workplace when I'm "the other person" that made them breakup. I feel alone in this. Some advice would really help me