Polygamy and adultery in your husband's case can be sidestepped by your husband. I cannot find any verse in the Bible that absolutory says that polygamy is a sin. Your husband can always say that he does not have lust thoughts or that lust only pertains to aMan lusting after MARRIED women. He can even say that no one knows his thoughts so there fore you can not prove his lust. The Bible is clear on a husband loving, showing honor, understanding his wife and giving himself up for his wife. Your husband likes to quote scriptures to back up his desire for intimate and physical affections with other women? If he really was that committed to scriptures then why doess he avoid the scriptures that talk about him loving you , understanding you, and giving up his fantasy for you? Reprinted below are a few scriptures that a person that really was committed to God's words would take into serious consideration. Likewise, husbands, live with your wives in an understanding way, showing honor to the woman as the weaker vessel, since they are heirs with you of the grace of life, so that your prayers may not be hindered.
1 Peter 3:7 Husbands, love your wives, as Christ loved the church and gave him up for her,
Ephesians 5:25 Your husband is more interested in himself and his fantasy rather than his Christian love for you or for his commitment to God's word. I think you are doing the best thing under the circumstances by separating from you husband. He is not living up to the standards of the Bible and has severely hurt your emotions by choice. You standing up for your honor and not enabling him are very admirable. Your actions may also help him to start breaking away from his selfishness and his ignoring God's word Sooner or later it is likely that he will get a rude awaking about his fantasies. He may even want you back to you but of course there maybe too much damage done or you maybe able to take him back if that are what you want. Your are hurting a lot right now so I hope that you can get some support from many sources.