Guess who's coming to dinner?

Have you or would you ever participate in a threesome? If two's company and three is a crowd why would you invite a third person into your bed? One late night you and your boyfriend have a discussion about your fantasies. He presents you with some Pandora's box shit like he wants to invite another woman into your bed. Of course you get to choose who she is. Or maybe he does depending on how receptive you are to the idea. You both agree on a girl and you go along with the plan. When things take off turns out she is more into you than she is to him. How ironic is that! Jealousy begins to rear it's ugly head and the situation hardly seems worth it. He has bitten off more than he can chew. Now his ass is choking. Does a threesome enhance or hinder a relationship?