The gemara today changes the rating of the storyline from PG to R. Mordechai instructed Esther to "visit" Achashveirosh willingly even though the consequence of this seduction would be that she can no longer return back to live with Mordechai. Regarding her relationship with Mordechai the gemara considers this to be a willing act of adultery. However, in her tefillah she asks why has Hashem left me, "maybe you are judging an o'nes like ra'tzon" - and rashi explains that although she is making a decision to go, it is regarded as o'nes since it is for the sake of saving the Jewish people. Regarding the aveira of adultery she is considered forced and not liable, but regarding her husband it is considered consentual adultery. The reason is found in the Beis Shmuel (Even Haezer 178) in the name of Maharik that although her action was not a rebellion against Hashem, she becomes assur to her husband since it is a rebellion against him (the pasuk of adultery being assur to her husband is "mu'ala bo ma'al" not "ma'al b'hashem").
R' Shlomo Kluger (E.H 178 in chochmas shlomo) tries to prove that although Yael did something similar to Esther by seducing Sisrah, she remained mutar to her husband from the fact that in shiras devorah it refers to her as "aishes chever hakeini". He then tries to make a distinction between Yael and Esther based on whether the adultery was an imminent and clear lead to saving the Jewish people. A tremendous chiddush!!
