Reading through the articles posted and felt I should post my own first experience having a MMF threesome with my girlfriend and my good friend.
It was a weekend, started out pretty usual way, hit the gym for an hour workout back home and into the shower. When I got out of the shower there was a text from an old buddy who had moved a couple hours drive away. He was going to be down and wanted to "play".
I told him I'd be home and asked how he felt about maybe having another person present, my gf. He reluctantly agreed as nerves were getting the best of him.
From there I started prepping her. She had no idea I was bi and no clue he was going to coming over that night.
We hung around doing odd things and on several attempts from her to play... After running about for a few errands and a quick bite to eat, we arrived home and I suggested she have a glass of wine and take a nice warm shower.
I poured the wine, she got undressed and threw a robe over her. I sat and chatted with her outside the shower talking dirty and playing a little with her nipples and pussy.
My buddy would be down in about five minutes, doors unlocked, all the lights off he was instructed to quietly get undressed and lay on the far side of our king sized bed.