Don't do it, especially if you think you love her. You will doom the relationship if you do.
Have you guys actually bothered to read the OP's profile? It says, and I quote:
Do you have a deep dark desire that needs release? We are a discrete couple looking for NSA fun. Uninhibited and willing to explore every fantasy. We will make your bed-time dreams come true.
Willing to travel and always play safe.
If he's actively trying to get a woman into their bed, then she has every right in the world to screw his friend.