The Rambam Hilchos Teshuvah 2:9 writes about what to do when asking for forgiveness from a person who won't grant it:
אֲפִלּוּ לֹא הִקְנִיט אֶת חֲבֵרוֹ אֶלָּא בִּדְבָרִים צָרִיךְ לְפַיְּסוֹ וְלִפְגֹּעַ בּוֹ עַד שֶׁיִּמְחל לוֹ. לֹא רָצָה חֲבֵרוֹ לִמְחל לוֹ מֵבִיא לוֹ שׁוּרָה שֶׁל שְׁלֹשָׁה בְּנֵי אָדָם מֵרֵעָיו וּפוֹגְעִין בּוֹ וּמְבַקְּשִׁין מִמֶּנּוּ. לֹא נִתְרַצָּה לָהֶן מֵבִיא לוֹ שְׁנִיָּה וּשְׁלִישִׁית.לֹא רָצָה מְנִיחוֹ וְהוֹלֵךְ לוֹ וְזֶה שֶׁלֹּא מָחַל הוּא הַחוֹטֵא
Even if a person only upset his friend by saying certain things, he must appease him and repeatedly approach him until his friend forgives him.
- a) If the wronged person doesn't want to forgive him, the person asking for forgiveness should bring a group of three friends and approach him with them and request forgiveness.
- b) If the wronged person is not appeased, the person asking for forgiveness should repeat the process a second and third time.
- c) If the wronged person still does not grant forgiveness, the person asking to be forgiven need not pursue the matter any further and on the contrary, now the person who refuses to grant forgiveness is the one considered as the sinner.
Two questions:
1) Why is the aggrieved party obligated to forgive the person who offended him, so much so that if he doesn't accept the 3rd apology he himself called a sinner? Maybe he was incredibly hurt!
2) The Rambam says that after the 3rd apology:
"the person asking to be forgiven need not pursue the matter any further"
Does this mean that even though his friend refuses to forgive him, Hashem forgives him anyway?