I accidentally [F]ucked [M]y best friend’s little sister

So I’ve known this girl longer than I’ve known my now best friend who we’ll call Jim. I actually met her back in a youthgroup when I was a sophmore and she was still in eighth grade. I guess I’ll call her Mary for this story… Even back then I kind of though she kind of had a crush on me. I’m not super attractive or anything but I had that generic skater haircut and girls digged that shit in the early 2000’s. Anyway, fastforward to my senior year in highschool and I had become quite good friends with her older brother and we’d hang out all of the time. At this point she had a boyfriend and we were just friendly. In highschool pretty much every guy and girl casually flirt I feel, so when we had little back and forths it was pretty normal in my experience. Mary was also very cute, was just the right amount of thicc and well endowed.