Strategies for getting over?

You know I’m not really sure how I’m gonna deal with this. It’s the first thing I think about when I wake up, and the last thing before I sleep, and everything in between too. My siblings are becoming more distant. I know they know. And my poor cousin. All I can say is this, there is absolutely no way I could knowingly do what I did. I was just a stupid kid. Only now as an adult do I reflect on my actions realizing the definition and gravity of them. I have OCD, it’s a terrible thing to live with. I feel like my potential in life is enormous, but this, this secret, this is a stone I can’t carry.

Having OCD/being a sensitive person while also having something that you deeply regret is a really challenging combo. To live a productive life again, you are going to have to tackle both issues on their own. By that, I mean you are going to have to learn to manage your OCD as well as go through the process of healing.
If you don't manage your OCD, you will never be able to look at your situation clearly or be able to fully process it to the point of forgiveness. To heal and move on from this you are going to have to forgive yourself.
We are all human and make mistakes. As much as I would love to hold myself to a higher standard, I cannot. No one can. I think you can especially forgive yourself for mistakes you made when you were just a kid. It would be wrong to think of yourself as worse than anyone else or to feel like you don't deserve forgiveness. The fact that this has tortured you so much shows that you are a good person. If a good friend was in your situation what would you tell them to do?
I think for decent people, forgiving yourself is much harder than forgiving others. But it doesn't mean that it's RIGHT to not forgive yourself. Just as it's not right to talk down to yourself, while many people who do that to themselves would never do it to someone else.
You have suffered enough over this and you need to focus now on healing, or else you are throwing your entire potential and life away - which will be by far far far the worse thing you'll have ever done.
But I suspect you would eventually come to these conclusions on your own if you weren't being jammed up by OCD. You really have to work on both things; forgiving yourself AND working hard to manage your OCD. All the epiphany's in the world won't mean anything if you don't retrain your brain to stop ruminating. There are a lot of great books on it out there, a lot of stuff online too. For me, I found understanding OCD took a lot of the power away from it. It helps you to see the patterns and predict it, and stop yourself from reacting to it. There are also meditations on forgiving yourself that might be helpful too.
Finally, I think the other thing that will help is time. Some self inflicted wounds take a bit to heal, but they do. But you also need to let them, by not picking at them constantly with OCD, or beating yourself down over it.