A man over time has a natural tendency to become bored with his own wife. When the Bible speaks of the "strange" woman, it speaks of the woman who is not your wife. Surely, "Bread of deceit is sweet to a man; but afterwards his mouth shall be filled with gravel" (Proverb 20:17). I will speak candidly here (and I will not be dogmatic). I do not believe it is a sin to practice polygamy. Hebrews 13:4 condemn adulterers and whoremongers, not marriage. God gave David Saul's wives (2nd Samuel 12:8). God never changes (Malachi 3:6). If polygamy was allowed in the Old Testament, it is allowable today. Unfortunately, modern heathen society will recognize sodomite relationships and fornication, but polygamy (marriage) is condemned.