How I [21M] cheated with my high school best friend (21F)

Hi everyone, it’s my first post on Reddit and english isn’t my native language so please tell me if something sounds weird !

The story I’m about to tell you happened a few years ago. I was hosting an Halloween party at my parent’s house (we have a nice place with a pool and not a lot of neighbors, so ideal to party !) and my girlfriend back then couldn’t come because she was studying really far away.

It was basically me, my sisters and 30+ friends of us, including some of my girlfriend’s friend and my best friend Anna.

Anna and I knew each other since the first year of high school, we used to take the same bus every day for at least 45 min. We always sat next to each other to talk, so we deeply knew each other personality, private and sex life.

She’s a petite blonde with a great body (I’d say a good B/ small C cups) and she exercise regularly. I’ve always thought that she was hot but never really wanted to date her because I knew she was not really the "faithful" type (sweet irony). But sometimes, listening again and again to her story describing precisely what she was doing with her body was a big turn on, I can’t deny.