Teshuvah and Yom Kippur only atone for sins between you and God, like eating a forbidden food or engaging in forbidden sexual relations. However, sins between you and other people... these will never be forgiven until you make good the damage you have done and appease the one you have hurt. Both things are required. It is not enough to repay stolen money, you must also ask the person from whom you stole the money to forgive you. Even if you have only hurt another's feelings through thoughtless speech, still you must appease the person and ask for forgiveness...

What if the other person does not desire to forgive you? Go back with three friends who will speak on your behalf and have them request forgiveness for you. If the other still resists, do this two or three times more. And if forgiveness is still withheld? Now you can step back and assume the sin is no longer yours. It now rests with the one who refuses to forgive. There is one exception to this: If the person you hurt was your teacher, you can never rest until forgiveness is granted. You must go back even 1000 times if necessary.

With regard to your being asked for forgiveness, it is forbidden for you to refuse to forgive. This is an act of cruelty. Rather, you should be easily pacified, and hard to anger. When a person asks you for forgiveness give it graciously with an open heart and a willing spirit. Do not seek revenge or bear a grudge. This is the path of Israel and those who are upright in spirit. [Maimonides,Mishneh Torah, Hilchot Teshuvah, 2:9-10]