I am very surprised at this, as I thought that in much of Africa traditional marriage customs were permitted to continue, just often not legally recognised. Is it the fact that he has one legal wife that makes it adultery? If you both were not "legal" wives but just traditional, would it be ok?
Even if the pastor IS right that God intends marriage to be only between one man and one woman, no other wives - he is also right that divorce is sinful. So the correct response would be to ask God for forgiveness for getting married - but now that you are married, to continue in that marriage without adding the extra sin of divorce.
Of course, the pastor is wrong. But whether he's right or wrong about God's intent for marriage being exclusively monogamous, what you should do now is the same - stay with your husband. Adding sin is never the answer.
You are not living in the Old Testament. You are living in Africa. In a country that was traditionally polygamous. You are living in the traditions of your ancestors. Traditions that Jesus did not teach against, and that Moses regulated. And you are choosing NOT to divorce, as Jesus very clearly taught against that. In fact, Jesus taught against divorce more strongly than Moses did. So by standing very firmly against divorce, you show that you ARE living under Jesus' teachings, and not just under the Old Testament!
While the Pastor is not living in the New Covenant. He is trying to persuade you to directly disobey the clear teachings of both Jesus and Paul, and sin by divorcing your husband. He is promoting serious sin. He is living in church tradition, not the Way of Jesus. And he is endangering his own salvation by doing so:
Matthew 18:7: "Woe to the world for temptations to sin! For it is necessary that temptations come, but woe to the one by whom the temptation comes!"
