Joining my best friend and her boyfriend [FFM]

Long time lurker and wanted to share my first threesome experience. This story happened in my mid-twenties with one of my best friends and her boyfriend, now husband.
My best friend and I were not strangers to hooking up with each other when this night happened. Her and I both had the epiphany that we were bisexual after multiple rendezvous in our early 20s but those are stories for another day.

This night happened shortly after moving away from Colorado and coming back for a weekend trip. I let my best friend know I will be in town and we plan a night to go out for sushi and have drinks at her and her boyfriends house. I show up at their house in the afternoon, we have a couple drinks and head to dinner. The whole time my best friend and I flirting with one another.

She assured me before going out that her boyfriend was very aware of our past and accepting of her preferences.