UPDATE: I was recently asked regarding the well known halacha that if someone who has hurt another in various ways - asks the victim three times to forgive and and the victim refuses - then the sinner is automatically forgiven and the victim becomes the sinner for bearing a grudge and holding on to hatred. It is claimed that this applies also to sexual abuse and furthermore that automatic forgiveness after 3 requests happens even if the abuser is not sincere in his apology! The simple answer is that according to most poskim it isn't so. Let me go through the sources.
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Shulchan Aruch (O.C. 606:1) based on the Rambam states: "Sins between men are not atoned by Yom Kippur but require that the victim be placated. This is true even if the sin was just verbal abuse. If the victim is not placated by the first apology then the sinner should return two and even three times. Each time he should bring 3 men with him. If the victim is not placated after the 3 apology then the sinner is not required apology to him again but should go before 10 men and ask for forgiveness. However if the victim of his abuse is his teacher then it is necessary to continue going to him many times until he is placated. Rema: The victim should not be cruel and refuse to forgive unless he refuses because he thinks it is beneficial to the one asking forgiveness [or to himself - Mishna Berura]. However if the sinner slandered him then it is not necessary to forgive him [and he is not considered cruel - Taz].
However we find elsewhere in the Shulchan Aruch regarding physically hurting another that there is no mention of apology - but that the judges force the assailant to placate the victim and that includes significant monetary payments. No mention is made of automatic forgiveness after asking three times but rather there is a requirement to pay money and the assailant is placed in cherem until it is paid - and this is not dependent on whether the apology is accepted..
Shulchan Aruch (C.M. 1:2): In the case of a man who hit another person, the judges lack the true semicha of Israel and therefore can not collect payment for nezek, tzar, pgam, boshes and kofer. However they can collect sheves and ripoi. Rema: And some say that even sheves and ripoi can not be collected anymore (Tur citing the Rosh). However I have not seen anybody observering this restriction. The standard procedure is that the judges force the assailant to placate the victim and the exact punishments according to that which seems appropriate to them.
Shulchan Aruch (C.M. 1:5): Even though that judges without the true semicha can not collect fines nevertheless they place the assailant in cherem until he placates the victim. As soon as he gives the victim an amount which appropriate then he is released from cherem (and this is true whether or not the victim has been placated). Alternatively if the victim himself forcibly takes that amount of money that is appropriate for him - the judges don't take it away from him. [...]
Shulchan Aruch (C.M. 1:5): Even though that judges without the true semicha can not collect fines nevertheless they place the assailant in cherem until he placates the victim. As soon as he gives the victim an amount which appropriate then he is released from cherem (and this is true whether or not the victim has been placated). Alternatively if the victim himself forcibly takes that amount of money that is appropriate for him - the judges don't take it away from him. [...]
Thus at least according to the Rema - physical assault does not have to be forgiven by the victim but the assailant is forced to pay that which the judges think is appropriate. Similarly slander does not have to be forgiven. That is because slander is difficult to undo since not everyone who heard the slander heard the apology. Finally, if the victim thinks it is beneficial either to himself or the assailant [Mishna Berura] not to forgive - he has the right not to forgive.
Furthermore the Rambam and Shulchan Aruch seem to go against the Yoma (23a) as pointed about by the Minchas Chinuch (241:1): Do not take revenge - Look at the Rambam (Hilchos De’os 7:7). However in Yoma (23a) it explains that this prohibition only applies in monetary matters but not matters involving bodily pain there is no prohibition of not taking revenge or not being spiteful. In the case of bodily pain it is only an act of piety not to hold a grudge. But the Rambam and also the Chinuch omit mentioning of this distinction and in fact it appears that they hold that one transgresses the prohibitions in all cases and this is a contraction to the gemora. Also look at the Rambam (Hilchos Talmid Torah 7:13) where he states that a talmid chachom that has been publicly embarrassed should take revenge and hold a grudge. See also the Kesef Mishna and the Lechem Mishna. Nevertheless no one commits a sin for taking revenge for personal suffering. I found in the Semag (11-12) who states that for personal suffering one does not transgress the prohibition of revenge and that this is learned from Yoma (23a).
[Updated section ]
It is apparently also the view of the Mishna Berura (156:4) that the prohibition of revenge and bearing a grudge applies only to monetary issues
Therefore the question remains why the Rambam and the Chinuch apparently rule contrary to the gemora.
Thus it is possible to understand that everyone - including the Rambam and the Chinuch - do not require forgiveness for non monetary abuse when it is too difficult. However that is only while the pain or embarrassment is still being experienced. However when the pain subsides and the victim is able to forgive - then it is possible that he will accept a sincere apology in order not to be cruel. Obviously if the apology is not sincere there is no need to consider it. With sexual abuse that time might never happen.
In sum: The requirement to forgive after three sincere requests therefore only apply to monetary issues where the victim doesn't experience serious emotional upset and trauma. In the case of non-monetary issues in addition there is the requirement for compensation which is required whether or not the victim forgives.
[Updated section ]
It is apparently also the view of the Mishna Berura (156:4) that the prohibition of revenge and bearing a grudge applies only to monetary issues
Therefore the question remains why the Rambam and the Chinuch apparently rule contrary to the gemora.
Rabbi Dovid Castle states in his excellent source book (To live Among Friends 28.42 page 913): "Most Poskim maintain that the sins of taking revenge and of bearing a grudge apply only to offenses related to monetary issues, such as refusal to lend something, but not to physical pain which includes degradation, lashon hara and embarrassment. For such matters bearing a grudge and taking revenge are permitted even if the offenses were not committed in your presence. For these matters it is only a measure of extreme piety not to bear a grudge or take revenge, but not an obligation. "
More relevant to the question of how the Rambam and Chinuch can ignore Yoma (23a) Rabbi Castle notes (28.47 page 926) [that even though the Chinuch prohibits revenge and grudges even for physical offenses the Chinuch (#338) also states that the Torah does not expect one to remain like a stone]. "Some say that everyone forbids taking revenge even for physical pain and embarrassment, but everyone permits bearing a grudge in such cases [of physical assault] because it is too much to demand from a person not to bear a grudge in such situations...." [He has much additional discussion in his chapter 28 on "Returning Hatred, Gruge, Revenge" pages 877-1043]
Thus it is possible to understand that everyone - including the Rambam and the Chinuch - do not require forgiveness for non monetary abuse when it is too difficult. However that is only while the pain or embarrassment is still being experienced. However when the pain subsides and the victim is able to forgive - then it is possible that he will accept a sincere apology in order not to be cruel. Obviously if the apology is not sincere there is no need to consider it. With sexual abuse that time might never happen.
In sum: The requirement to forgive after three sincere requests therefore only apply to monetary issues where the victim doesn't experience serious emotional upset and trauma. In the case of non-monetary issues in addition there is the requirement for compensation which is required whether or not the victim forgives.
