I will think that despite the gravity of the mistake, since it
is a one-off incident and you can be a good wife, you may decide to
forgive yourself. Keep this secret to yourself, if possible, forget
it. Of course, quit. Go back to your bf and get married and live a
happily married after life.
However, since you are prepared to leave with the consequences of
your action, and have decided to leave him, why tell him the truth
to hurt him more? Do you know that the truth will hurt him
alot?
why not just leave him quietly?