And we never talked about it again...........

Is the past really worth going back to?  I have a major life event that happened to me at age 15; I think about it most every day.  There is another person involved and there was zero closure.  Obviously as a teenager you don't really have that ability.  I talked to my therapist about it because I feel like I need forgiveness.  Do I need forgiveness from this other person involved? He automatically is in my thoughts when I think of this event.  I decided to send him a letter....almost 20 years after we have seen each other.  I can't imagine the shock on his face when he sees the return address, but a letter will get to him by the end of the week.  I don't necessarily expect a response, it would be nice to know that he is 'okay' with it.  Funny, how I ask that when I am not really okay with it. No one ever talked about it in my family and him/I never did either.  Is that why I still think about this emptiness I feel.