Yosef Karo

“ If he is one's rabbi, one must go to him several times until the rabbi is appeased. Rem"a: One should not be cruel and withhold forgiveness (Mahari"l) unless it is for the benefit of the one seeking forgiveness (Gemara Yoma) . If one was a victim of slander, one need not forgive (Mordechai and Smag and Hagahot Maimoni in chapter 2 of the Laws of Teshuvah and Mahari"v) . ”

“ Shulchan Aruch Orach Chaim 606 Reconciling with friends on Erev Yom Kippur
שיפייס אדם חבירו בערב יום כפור
606:1 Transgressions between people are not subject to atonement on Yom Kippur unless the offender appeases the offended party. Even if one aggrieved another with words alone, this appeasement is necessary. If one cannot effect appeasement at first, one must return a second and a third time, taking along three people each time. If the offended party will not be appeased after three visits, one may desist. ”