The Bible does not support polygamy. The most one can say is that the Old Testament describes polygamy. And when it does, it doesn't cast polygamy in a good light. While it may have been a culturally accepted practice perhaps picked up by the neighboring nations, nowhere does God condone it. Most instances of the patriarch's polygamy resulted in problems (see Abraham, Jacob, David). In 1 Kings 11, Solomon's polyamory (many loves) and polygamy (many wives) turned his heart after other gods and was in direct disobedience to God. Verse 6 says it was "evil in the eyes of the Lord." I assume the Romans 7 passage you mentioned is Romans 7:1-6. In that section, Paul is explaining how we are freed from being bound to the law (to now serve Christ through the power of Spirit) using marriage as an illustration. Since we are united with Christ and Christ has died to the law, so now we are free from the rules of that relationship. Just like when someone’s husband dies, then and then only is the wife is free to marry another. If she has sex with someone who isn’t her husband while still being married, it’s adultery. Again, Paul’s use of marriage is illustrative for the purpose of talking about the law. It is not in any way condoning polygamy. In Matthew 19 what is in view here is Jesus being pitted between two popular Rabbinical ideas on divorce. The House of Hillel taught that a man could legally divorce his wife for “a thing of immorality,” which was their own interpretation of the Mosaic Law on divorce. This quickly led to an “any cause” divorce being permissible. The House of Shammai taught that a husband could divorce his wife on the grounds of sexual immorality. Jesus doesn’t take the bait. Instead he reminds them of God’s original design: two becoming one flesh. While you may be right in suggesting that only men are in view in Matthew 19 with regards to initiating the divorce, it's important to note that Mark’s gospel records Jesus as including women in the prohibition on divorce. In either case, polygamy is not in view and is in no way supported by the texts.