[ See views of Rav Pe'alim] Rav Yisroel Yaakov Fischer (Even Yisroel 8:85): Question: A baal teshuva who had returned to Judaism a number of years ago came to me. There remained one thing that bothered him greatly about his past and that was the fact that he had a relationship with a married woman. The question that he was upset about whether he was obligated to tell the husband about his wife’s sin to save him from sinning - since she had committed adultery willingly. The dilemma was that if he told the husband that would destroy the reputation of the family since it was a distinguished family. However if he didn’t tell the husband then he would be responsible for the sins that the husband has constantly since she is now prohibited to him.
Answer: This question was addressed already by the Nodah B’Yehuda (Tenina O.C. #35). He said it depended on a dispute between the Rambam
and the Rosh. The
Rambam ruled in Hilchos Kelayim (10:29) that if one sees someone wearing kelayim that is prohibited by the Torah he is required to rip it off the other person – even in the street and even if the person is his teacher who has taught him wisdom. It is clear that the opinion of the Rambam is that this must be done even if the wearing of kelayim did not do it deliberately and in fact is not aware that he is wearing kelayim. Nevertheless it must be ripped off of him without concern for the person’s dignity. The Shulchan Aruch (Y.D. 303) agrees with the Rambam. In contrast the Rosh (Nida 9:6) brings the words of the Yerushalmi
)Kelayim 9:1),... The Rosh explains,”Rav Ami follows the view of the Amora who permits and it is in a case where either the kelayim is rabbinic or he holds that only in the case where a person finds kelayim in his own clothing he must rip it off because
'there is no wisdom or understanding against G‑d commands.
' In contrast if a person see kelayim prohibited by the Torah on another person and that person doesn’t know about it – he should not inform him while he is in public because of human dignity since he isn’t wearing it on purpose to violate the Torah.” Rema (Y.D.#303) agrees
with the view of the Rosh and he states, “And some say that if the one wearing the kelayim is unaware of it it is not necessary to tell him in public.” Therefore the Noda B’Yehuda says that the question is dependent on this dispute. The Rambam’s view is that even if the person is unaware that he is sinning the prohibited kelayim still must be ripped off of him even in public and we are not concerned with his dignity. The Rambam would hold in our case that it is necessary to tell the husband in order that he separate from his wife who is now prohibited to him because the husband is doing an active act which is prohibited. In contrast the
view of the Rosh is that when someone is not sinning on purpose it is not necessary to tell him if this leads to him being embarrassed and degraded. Therefore in our case he would hold that it is not necessary to tell the husband since he isn’t deliberately sinning. However the Noda
B’Yehuda adds that our case
is different from that of kelayim. That is because the unaware person is not sinning just once but he will continue to sin for a long time. Consequently he asserts that even the Rosh would agree that it is necessary to inform the husband [....] Due to the various factors mentioned it is certain that there is no need to inform either the wife or the husband that they are prohibited because of adultery - because it won't result in their divorce. In addition there is the factor of human dignity. Furthermore one can say that even according to the Rambam in this case he would not require informing them since he doesn't witness that they are having prohibited relations and also it is possible that they won't be having sexual relations as is mentioned by Rav Pe'alim and other achronim agree with him.
Rav Wosner also has a tshuva on this subject and relies on Divrei Chaim not to tell husband and even if he does tell the husband they don't have to get divorced unless the husband believes him.
Rav Wosner (Shevet
Halevi 8:287.1): Concerning a baal teshuva who unfortunately had a
relationship with a married woman. Is there an obligation for the baal teshuva
to tell the husband who is an observant Jew in order for him to separate from
her since she is prohibited to him? I can’t go into detail in this matters but we
typically follow the view of the Divrei Chaim (O.C. #35) who permits hims to
turn a blind eye. According to this principle, even if he tells the husband, the
husband is not obligated to divorce her unless the husband believes the
testimony as is stated in Shuchan Aruch (E.H. 115:7). Consequently as long as
he doesn’t believe her she is permitted to him according to the halacha. In
such a case where he is not going to believe the testimony, it is permitted for
the person not to inform the husband. Look at the Divrei Chaim itself.
Even Yisroel 8 85 Report Adultery