regret?

what's regret actually means?
something that you feel terribly sorry after doing it, and would do anything to go back to repair broken things?
nobody's perfect, I mean everybody makes mistakes, right?
is it worthy to giving someone who already broke your heart into pieces a second chance?
the Mighty God's always giving a mercy to His mankind. but, why forgiving just one person is so hard?
ok, maybe forgiving is easy. but to forget? it'll need days or weeks or maybe years to forgeting something bad. the scar will stays forever.

oh God, please teach me more about forgiving and forgeting. I'm so zero about it..