Hockey Game and Some Friends [MFM]

Please forgive me if the timeline is a bit out of order, this recollection needed a bit of liquid courage to share.

One night, pre-Covid a bunch of my friends got together to go see a hockey game. My girlfriend at the time had decided to go have a few drinks with her girl pals, so we had the perfect opportunity to spend time with each of our friend groups. In separate groups we had decided to send some risqué texts and to be flirty with each other throughout the course of the evening.
My gf and I have always been open to the idea of enjoying each other’s friends and bringing others into our “sexy time”. Throughout the game I mentioned to a friend, let’s call him “M”, about the idea of having some fun with my gf. He is an athletic guy, about 5’9”, and in really good shape as a former college soccer player. He really enjoyed the idea and wanted to give it a go. We had started a nice little conversation through text with the three of us, being flirty and mentioning the great time we could have. After a bit of alcohol, and a great hockey game, we decided to reconvene at his place. We start to take shots and really get into the the mood to have some fun. Some background on my gf and I. She’s 5’6, redhead, incredible slim waist and fat ass. I’m 6’1”, a decent bit of muscle mass and an average sized bit of fun.