OCD has nothing to do with guilt. Don't know if you actually have OCD or not, most people on this forum don't seem to. Anyone can have guilt. You don't need to be an OCD sufferer for that. As for what you did when you were 12 and your cousin was 9, people develop sexuality at very different ages. You don't say if you used persuasion on your cousin or she was a willing participant, but hey, either way, you were kids. It doesn't sound like any harm was done, just some role playing. Kids do that. You erased the video, so it's not floating around on the internet, which you would justifiably feel guilty about. You didn't abuse her, which you would justifiably feel guilty about. If it happened as you say, stop being so hard on yourself. And how did she turn out? Ever talk about it? Or did you both more likely just forget about it and go on being kids?