First, it’s important to remember that this all happened when you were 15, over half your life ago. Your parents were in a complicated relationship that was characterized by violence and heavy drinking on both of their parts. As a teenager, you could not be expected to know how to intervene. You acted only like most kids would act — frozen and unable to make sense of what was happening. You aren’t the same person now and would behave differently. But you can’t judge your younger self for being scared and disbelieving and unable to act.
It is to your parents’ credit that they could both be loving parents even though they could not be loving mates. You are the sensitive man you are because they loved you in spite of their inability to love each other. Please don’t lose sight of that.
Your sister characterizes the event as a rape. She may be correct. She might not be. I can think of a number of ways to understand the story. Please don’t misunderstand. I don’t think rape is ever okay. But neither one of us knows what really happened.
I think the person you need to be talking with at this point isn’t me or your sister. It’s your parents. You can ask them their versions of what happened that night and what they think about it now. It may be that there is more to it than you currently understand. They may have had to scare themselves with more violence and name-calling to finally realize how bad things were so they could finally separate.
You can certainly tell your folks how their fighting affected you. You can share with them how frightening it was to hear your mother screaming. You can tell them how confusing it has always been to see their loving side and then remember the violence. Most important, it’s appropriate to ask them to apologize for what they put you and your sister through.
Once you have more of the story; once you have tried to be understanding and understood – then you can decide if you are ready to forgive them and to try to make a relationship with them as they are now.
Whatever happens with your relationship with your parents, I hope you will find a way to move on for yourself.
I wish you well.