This is because you are young. Some life lessons take a period of adjustment and this is one of those situations.
There is no hard and fast legal rule that says you are ever 100% safe. I could say 6 years and you'll groan and feel despair and think about how unfair the legal system is, but that is not the way to view it.
Yours is an internal issue, not legal. Accept the situation for what it is and stop worrying about it. Worry will not change anything.
Maybe look at coping techniques if can't sleep at night.