There is a sex trafficking case currently in the news. If a sex-slave gets saved, would she loose her salvation because her circumstances prevented her from leaving her "job"?
If a prostitute were to get saved, do you believe that the Holy Spirit is capable of changing the desire of her heart so she would want to do some other "job"?
To answer directly, yes ... God will forgive her while she keeps her job and God will continue to work on her heart to change it so that soon she will want to quit that job. I was saved while entangled in criminal activities and God still honored my salvation while an arsonist and a drug smuggler. "God loves us just as we are, but he loves us too much to leave us there." I can testify to the truth of that statement.
You have not proven that a marriage between a believer and an unbeliever is a covenant marriage with God. As I have explained Paul indicates otherwise. Until you refute that with more than opinion and fiat, there is no evidence that there is adultery.
In those cases where there is 'adultery' (per Jesus statements), there is no evidence that God cannot forgive a believer who obeys the command to confess the sin. Once forgiven, the sin of divorce and the ongoing adultery are "under the blood of Jesus" and "remembered no more" and "as far as the East is from the West". You have given no evidence from scripture that this sin is UNFORGIVABLE.