Sexual encounter with my cousin.

Warning: This is my confession, and it is a wall-of-text, and there will be no tl;dr. I'm sorry. She was actually my step-cousin, but that doesn't make this any better. I am a male. I don't remember how old I actually was. Probably around 11-13 years old... if I was older, it was not by much. She was around 7 or 8. I had had a slight attraction to her, and I had been indulging it by holding her hand occasionally. That was about the extent of it... until this particular encounter. I was in the basement, on the couch, watching television with her (we'll call her Jessica) and her older sister (we'll call her Jane), who was still younger than me. I don't remember what caused her to do this, but Jane told Jessica to do some sort of trick... or something. Jessica knew exactly what she was talking about: she climbed on top of me, straddling me, and then slowly moved up my body so that her crotch was essentially smothering my face. She was fully dressed, but I was still turned on like no other. I'm pretty sure I knew a decent deal about sex by then, so I knew the exact nature of what she was doing, the exact way that I was enjoying it, and why it made her feel good. She was more innocent, it seemed, she was just laughing and thought it was funny to put her crotch in her cousin's face. I allowed this to continue for as long as she wanted, even pretending to be confused and bothered: I would pull my face out, say "what? What's going on?" or something to that effect, and then put my mouth right back on her crotch. I know she was the one who initiated the act, but she was young, and much more innocent than I. I allowed it to happen, even when I knew what it really was. I would never do something like this again...never. I would never touch a child, never take advantage of an innocent like that. I truly think that I did not realize the wrongs in taking advantage of someone like this. If I had, I don't think I would have let it happen. Nevertheless, this instance plagues me. Does she remember it? Has it affected her negatively? Has this scarred her, and does she think of me as some sort of a monster? I sort of feel like one.