Please stop beating yourself up. You are sorry; you should make amends to the cousin -- who undoubtedly does remember -- so that you can open this festering wound, heal it, and move on. I am pretty sure you would not have done this had you not been abused yourself. In some strange way, victims tend to become abusers or to be victimized again unless something happens (therapy, 12-step group) to stop the cycle.
Don't beat yourself up any more. This only perpetuates your abuse.