THREESOME PART 2

So I mentioned a few days ago my bestie wants me to join her and her man in a threesome. I've been asked by her a few times but she changes her mind. So were supposed to do it this weekend but I'm guessing it won't happen...what should I say to her? I don't want her man at all and I've stated that. She said it could be just a me n her thing and he could watch. Or not. I feel like it's just a fantasy...so how should I talk to her about it?