threesome?!?

Ok my BF has this fantasy with me and another chic.!! Yeah I know all guys have this fantasy... well I’m ok to give it a try but he is proposing this chic which I said no bc it would be awkward since she works in the same place as we do...anyways he asked me to look for a chic. I’m not sure 🤔 should I go through this or definitely say no?!? Have you done it before if so please share your experience.