פירוש על עבודה זרה 45:2

The Talmud tries to use two seemingly contradictory mishnayot to demonstrate that there is a difference between ab initio, when we are not concerned for sexual misconduct, and ex post facto, where we are not concerned. Ab initio a woman should not be alone with non-Jews — we fear that they will rape her But ex post facto, if she was alone with them because she was imprisoned for monetary matters, then she is still permitted to her husband. We are not concerned that she willingly had sex with them (which would cause her to be prohibited to her husband, even if he is not a priest).