Commentary for Genesis 39:9

וחטאתי לאלהים AND SIN AGAINST GOD — The “Sons of Noah” (בני נח) were subject to the command which forbade immorality (Sanhedrin 56b).

AND I SHALL SIN AGAINST G-D. The Sons of Noah²²⁵See Note 113 above. were commanded concerning forbidden relations. This is Rashi’s language.
This is correct. It is only due to the feminine lack of knowledge that he first told her that the act would constitute a betrayal of his master who trusted him, and following that he added that it also involves a sin against G-d.
It is possible to further explain the verse, And I shall sin against G-d, by this betrayal, since “it would be a matter of great evil consequence which would be accounted to me as a sin against G-d since His eyes are upon the faithful of the land,²²⁶Psalms 101:6. and no traitor dare come before Him.” Joseph spoke the truth. However he did not mention the prohibition of the illicit relation²²⁷According to this interpretation. because he spoke in language suitable to women.

כי אם אותך באשר את אשתו, the only restrictions imposed upon me in this house concern the inviolable marital relations between you and my master, your husband.