I find it interesting, but a little unnerving, that both Jesus in Mt. 19, and Paul in 1 Cor. 7 have different rules for women, than for men. Did you ever notice that?
I doubt I can add anything to what you already know but I will have a go.
In Matt and Mark, Jesus was transitioning the law into a more spiritual phase. In the past "adultery" by the man against the wife by divorce (Mark 10:11) had been allowed because men's hearts were hard. Jesus said of his new teaching respecting divorce by man, "All men cannot receive this saying, save they to whom it is given. He that is able to receive it, let him receive it." Mat 19:11.
So the law of divorce under the spiritual regime is similar for men and women Mark 10:11,12.
In the case of adultery with another man's current wife the sin is more serious: Deu 22:22. The adulterer commits a criminal offence under the law of Moses. It would mandate excommunication from any "church of God." If he is admitted to a church, it would not be by a church "of God." Not every church is Christian. A church that admits unrepentant adulterers is not a Christian church.
39 A wife is bound by law as long as her husband lives; but if her husband dies, she is at liberty to be married to whom she wishes, only in the Lord. 1 Cor. 7
I think this is not referring to the situation where the marriage has been repudiated by the heathen husband, not only because the "husband" is no longer "her" husband but someone else's, but because the heathen has no interest in reconciliation or in repentance. The unbinding has occured in respect of the heathen, by token of his heathenism. I think this is a practical teaching. Note 1 Cor 7:15 "If the unbeliever leaves, let it be so. The brother or the sister is NOT BOUND in such circumstances;"
Mat 5:32 is relevant in the theocracy, and to believers. Jesus acknowledges that a woman divorced will (eventually) "commit adultery" as will the man who marries her, but that the adultery is caused by the divorcing party. This means that the divorcing party bears the responsibility for the guilt of the adultery of the divorced person and their spouse in a theocracy. Yet what does Jesus mean by "adultery" in respect of a heathen repudiating a marriage? Marriage is only for believers. It has no application to heathens. Marriage itself is a theocratic institution.
And "theocracy" is the context here. Matt 5:32 is relevant to rthe theocracy of Israel (i.e believers in the church). It is a theocratic law he has set in place, i.e intended for those living under the theocracy. Jesus was angling for reconciliation in the theocracy and condemning as adulterers anyone who hindered reconciliation by marrying a divorced woman, or a woman who hindered reconciliation by getting re-married. This teaching is reflected in 1 Cor 7:10,11.
Whereas Paul then considers the issue in terms of the divorcing party not being part of the theocracy (the church). 1 Cor 7 is talking about heathens who renounce marriage. That is different. Heathens are nasty people, and to be treated differently. As before 1 Cor 7:15 applies. As for you, you said:
"My Christian husband divorced me to marry the wife of his best friend. They caused two divorces, but for me I am still bound and after 20 years, he is still the last may I kissed. I WILL NOT sin."
As I have said above, your husband is not a Christian, because he committed adultery with another man's wife. He is a heathen. 1 Cor 7:15 applies. You are NOT BOUND and you will not sin by getting remarried.
