My gf and her best friend

Ok. I’m a 22 year old girl and just got back from Chicago with my girlfriend and we had a good time with her family. Christmas was amazing. Christmas sex was amazing. 3 hours later a knock on the door and is walks my girlfriend's best friend since 3 grade. 5'4, black hair, hour glass body, golden brown tan, dark blue eyes. This girl's presence just screams sex. My girlfriend gets all excited and happy. Which is fine, after all it's her best friend that she hasn't seen in years. They hug and I let my girlfriend know not to tell her that I'm her gf just because I didn't know how she'd react.
I get introduced she looks at me for a good 10 seconds and then smiles. Next thing this girl is all over my gf. She figures it and asks my gf why she never let her have sex with her. Wtf
So my gf says why dont we all get undressed now and she can taste her for the first time. This girl cant get undressed fast enough. I look at her body and just want to put my fingers inside her so we all get naked and fun begins. We spend the next 5 hours licking fingering and making each other scream with pleasure.  Then she left and said we’d never talk about it again.