Love is the only answer to any question.
It is very hard to forget the past and so asking someone to forget the past is almost impossible. What the main issue should be, is to Forgive the past. Look to the future and believe in the person you are with. If by actions and words they are trying to recreate a new beginning, one must take the first step to trust that what they are trying to do is honest. People are only human and by being so, they make mistakes.