Some years ago I committed a very evil sin.

Answer

As long as you have regret and you repent, Insha-Allah, your past sins will not be exposed. Occasionally renew Taubah. Forget about the past sin. Make dua for protection. Recite YAA SAT-TAARO frequently. This is one of the Names of Allah Ta'ala. It means: O You Who are the Concealer of sin! Allah Ta'ala always conceals the sins of the true repenter. Rasulullah (Sallallahu alayhi wasallam) said: "The true repenter of sins is like one who has no sins."