I [19M] spontaneously fisted my ex gf’s [18F] asshole [MF]

So this must’ve been January. We were just kissing, not really doing anything sexual since her whole family were in. She often sat on top of me just sitting on her phone; facing me sometimes and sometimes with her ass in my face. It was a strange little thing but it was nice. On this day I had the horn. Like A LOT so when she had her ass facing me I couldn’t help myself. I started taking her bottoms down a bit. She really appreciated this and got up a bit to allow me to take them down more. We both liked anal a lot so I started playing with her ass and getting her to lick my fingers after etc. It was really hot and we could somehow do anal pretty well with just spit, no lube.