Thank you for writing. You don’t need to be haunted by this for the rest of your life.
My guess is that your sister was also abused by the cousins. She probably didn’t like what was happening and may have known it was wrong but her body responded with pleasure. How does a kid reconcile those conflicting things?
Children, like maybe your sister, often try to resolve confused feelings by copying a disturbing behavior in an attempt to figure it out. This is termed a “behavioral reenactment.” The child isn’t consciously aware that that is what they are doing. It’s an instinctive effort to come to terms with a traumatic experience.
Further, many victims of childhood abuse go on to have abusive relationships, either as a victim or as a perpetrator. The reasons are very complex but, simply put, they often ratchet between the two roles because they don’t understand that physical pleasure can happen without abuse being part of it.
Let’s remember that you were both children who were being exploited by the cousins. The two of you were and are in the same boat. You were both victims. Chances are, you are both still reverberating from the experience. It’s possible that she is as anxious about it as you are and that she also doesn’t know what to do about your mutual history.
Instead of hating her, talk to her. Approach her with compassion, not anger. She may be feeling guilty. She may have tried to minimize or push away things that happened during that time out of confusion, shame, or fear. She may be relieved to be given the chance to clear up any tension that exists between the two of you as a result.
If it feels too difficult to you to initiate such a talk, seek out a family therapist who can help you. Start by going to sessions by yourself to talk about your experience and to rehearse how you will talk to your sister. The therapist will provide you with guidance and support. In your case, the conversation with your sister isn’t a “confrontation”. It as an effort for both of you, together, to resolve a childhood experience that never should have happened.
I wish you well.