My perspective is a little different in that I think its time for you to take care of YOU, first and formost. The silence has gone on long enough. Telling or not telling, and how much to tell, should be based on whats best for YOU. Not anyone else. You no longer should protect anyone else from the truth of what happened, not at the expense of your own healing.
This may sound hard, but if you decide to tell your parents, it should be because it will be healing for YOU, even if it is hurtful for them. They are the PARENTS. They are the ones who should be doing the accepting, loving, comforting, and protecting. Its should not have been your job to comfort them then, and its not your job now.
Your job is to decide who, if anyone, you need to tell to move yourself forward in recovery. And to decide what, and how much to tell. You are in control of your life now. Don't sacrifice yourself anymore. You deserve to be a whole healthy man. Do what you have to to get there. Thats my opinion.
"And God only knows
God makes his plan
The information's unavailable to the mortal man
We're workin' our jobs
Collect our pay
Believe were gliding down the highway
When if fact we're slip slidin' away"Paul Simon