משנה אויף במדבר 5:29

A betrothed woman and a shomeret yavam do not drink [the bitter waters] and do not receive their ketubah, as it is said, “When a wife, being under her husband, goes astray” (Numbers 5:29), this excludes a betrothed woman and a shomeret yavam. A widow who had married a high priest, a divorced woman or a halutzah who had married an ordinary priest, a mamzeret or a netinah who had married an Israelite, and the daughter of an Israelite who had married a mamzer or a natin do not drink [the bitter waters] and do not receive their ketubah.

Just as the water checks her so the water checks him, as it is said, “And shall enter”, “And shall enter” (Numbers 5:22,. Just as she is prohibited to the husband so is she prohibited to the lover, as it is said, “defiled … and is defiled” (Numbers 5:27,, the words of Rabbi Akiba. Rabbi Joshua said: thus Zechariah ben Hakatzav used to expound. Rabbi says: twice in the portion, “If she is defiled…defiled”--one referring [to her being prohibited] to the husband and the other to the paramour.