Best friend threesome

So, I have a best friend who has a boyfriend and their in a open relationship. Her boyfriend had hit up on me before and I shut it down because she was my best friend and I thought it was wrong and before I know they were in a open relationship. They’re still together and they’ve had threesomes with his friends, but now I actually want to be included. I don’t know if I should tell her. I don’t want to be rejected and humiliated. I’ve tried to text him, but the subject doesn’t go the way I want it. Is this a bad choice I’ll be doing? Like I’m craving the sex, and I’ll be open to be FWB, but I’m scared of her not wanting ME.