Last night something crazy happened

My gf and her gorgeous little sister got really drunk and when I went to bed the little sister jokingly got in too so I was in the middle of them.
The joke got serious when they both ended up passing out.
I started feeling the sisters body, she was in a skirt and singlet. After a while of touching her all over it seemed she was pretending to be asleep but was making little moans like she was enjoying it and in the moment her body language was definitely saying she liked it.
I ended up going under the blanket and eating her pussy, I sucked her boobs and when I heard my gf snoring I climbed ontop of the sister pulled her panties across and pushed my cock into her little pussy.
Slowly and steadily I fucked her trying not to make big movements. She was making quiet little moans and kept her eyes shut the whole time pretending to be asleep.
This morning was so awkward but besides claiming to have a hang over she seems fine.. My gf has no idea and im feeling fucking great :(