1) THE HUSBAND'S "MECHILAH" OF HIS "KINUY"
QUESTION: The Gemara says that the husband may forgo his Kinuy and prevent his wife from becoming prohibited to him through Setirah with the suspected adulterer after the Kinuy. The Mechilah of the Kinuy renders the Setirah nothing more than a transgression of the Isur of Yichud, which does not prohibit her to her husband since she has a Chezkas Kashrus that she is innocent of sin.
One Amora maintains that the husband may forgo the Kinuy even after his wife did Setirah and thereby permit her to him retroactively. How does the husband's Mechilah of his Kinuy permit his wife after the Setirah? The reason why the woman becomes prohibited to him when she did Setirah after Kinuy (as opposed to Setirah without Kinuy) is the logical argument of "Raglayim l'Davar" (Nidah 3a): since the husband warned her not to seclude herself with this man and informed her of the consequences, she would not have secluded herself with him unless she had a strong Yetzer ha'Ra to sin with him, and thus it may be assumed that she sinned.
The Mechilah of the Kinuy does not remove this logical argument. She still should be prohibited to her husband because of "Raglayim l'Davar" that she sinned. (REBBI AKIVA EIGER)
(a) RABEINU CHAIM HA'LEVI
answers that "Raglayim l'Davar" alone does not suffice to prohibit a Sotah to her husband. The Chezkas Kashrus would overpower even the "Raglayim l'Davar" and permit her if not for the special Gezeiras ha'Kasuv which teaches that when a woman is Nisterah after Kinuy, she becomes prohibited to her husband. Therefore, when the husband forgoes the Kinuy, the woman is no longer prohibited to him. (See Insights to Sotah 18:1
(b) Perhaps the Mechilah of the Kinuy indeed weakens the proof of "Raglayim l'Davar." The woman may have known that the husband's Mechilah of the Kinuy is effective, and she may have planned to persuade her husband to be Mochel the Kinuy and permit her to remain married to him. As a result, she knew she did not risk very much by secluding herself with the other man after the Kinuy. She may have felt free to seclude herself with him without sinning, and therefore there is no "Raglayim l'Davar."
This situation is comparable to Kinuy done without witnesses, which the Gemara (2b) implies cannot prohibit to her husband even though both know that there was a Kinuy. (See the TESHUVOS SHA'AGAS ARYEH, Hosafah 1.) Why should she be permitted to him if she was Nisterah after such a Kinuy? She should be prohibited because of "Raglayim l'Davar" since they both know that there was a Kinuy! The answer is that she was not afraid to seclude herself after such a Kinuy since she knew that the consequences would not be so severe, for she could simply deny that there ever was a Kinuy and no one would be able to disprove her.
(c) Alternatively, if the husband was Mochel the Kinuy, it is assumed that he investigated the matter and determined that his wife did not sin with the other man. This Chazakah is based on the assumption that a husband normally does not desire to return to an unfaithful wife. The fact that he was Mochel the Kinuy and wants to return to her indicates that he investigated the matter and found her innocent. (This Chazakah is similar to the Chazakah of "Ishah Daika u'Minseva" (Yevamos 25a), which states that when a woman remarries based on the testimony of a single witness who says that her first husband died, it is assumed that she remarries only after she has thoroughly investigated the matter and knows that the witness is telling the truth.)
This Chazakah offsets the proof of "Raglayim l'Davar" which states that she sinned, and therefore she is permitted to her husband. (M. KORNFELD)