A very harrowing experience! There are lots of facets involved in telling them. The first is what would the benefits to you, in particular, would it liberate you to a large extent from that weight of the past? It would seem not. You say nothing that iudicates that.
Secondly would it benefit your parents after all this time? It seems the only thing they would gain is undertsanding why you went of the rails, but, as you said yourself, they couldn’t handle it. Therefore it is more to their detriment.
On the basis of those two fundamental things then the answer is clearly that you say nothing, in effect its too late. However, its not too late for you to hope for a more normal life. You mention nothing about seeking professional help to deal with this since you were at the age of majority, so its sounds like you haven’t.
Going the shrink route for such a deep trauma so long ago would take far too long, even if it succeded and there is no guarantee that it would. Only going from what you said here it would appear that guilt for not having said something at the time and even since has lowered your self esteem to the point that you don’t much care about yourself. Yet it was not your fault that what occured occured. That would seem also to block you doing exercizes that I could suggest for reprogramming your subconscious to restore that esteem.
I believe that it can be restored if you go and see a MEDICAL hypnotist and you agreed a programme together. Such a perzson has the capacity to transform the way you view and remember things and the consequences. Please try it!