1,816. When Intimacy is Not Considered Promiscuous
Hilchos Geirushin 10:16
The women in the previous halachos are permitted to marry the son of the witness who testified about her, the son of the Torah authority who declared her prohibited to her husband and the son of the man with whom she was alleged to have had an improper relationship, as well as any other male relative of these individuals. We are not concerned about the possibility that a person might commit a sin in order to benefit someone else. A woman is also permitted to marry one of the witnesses to her divorce or to her refusal (of a marriage arranged by a minor orphan’s relatives), as well as one of the judges in front of whom she performed chalitzah (the shoe-removal that severs the bonds of levirate marriage). We are only concerned about a witness who testified to permit her. One should try to avoid serving as a witness to refusal but make himself available to serve as a witness for chalitzah. (Talmud Yevamos 109b says that one should avoid refusals because the minor girl might grow up to realize that she rejected a good match.)
Hilchos Geirushin 10:17
If a man divorces his wife and they subsequently engage in intimacy with witnesses before she marries someone else, we assume that their intention is reconciliation and their intimacy is meant to effect betrothal rather than a promiscuous act. This is true regardless of whether they divorced after marriage or after betrothal, and even if we saw him give her money. The presumption is that a man will not engage in intimacy with his wife promiscuously if he has the option of their relations being considered a mitzvah. Because of this, the woman in question is considered definitely betrothed and must be given a second divorce.