Feeling guilty is natural.

Quite often we can only see the evil of what we did in retrospect.
That's a fact.
We do something to someone and we hurt their feelings. We may or may not have known of the impact at the time of the occurrence. Now we do. Now we feel guilty.
Doing something to someone to hurt them physically is just as awful.
Guilt.
That feeling of guilt is horrible.
What to do?
As adults, we resolve to improve our treatment of ourselves and others.
As adults, we know we cannot make amends, but we can do better starting here and now.
As an adult, I promise to do better.
As adults, we cultivate the discipline to live a life that reflects our commitment to being the best human beings that we can be.
As adults, we think for ourselves.
Great deeds have been accomplished by seemingly horrible people.
We are human beings on a path to becoming perfect.