There are different views about Queen Esther. Some Christians say that marriage after divorce in the church is OK because Esther was a godly woman who was married to a divorced man in this Bible story. But others say that although this is the case it does not mean that God approved of this sinful relationship with her husband. But the truth is none of these, it is actually a very short and simple answer. I do believe that Esther was a godly woman and although the King was a heathen I do believe that he was a good man also. Although everyone seems to think that the King divorced the former Queen to marry another wife, this is not the case. There is no mention of the King putting away the Queen, but rather she was simply no longer to come before the King any more and her royal estate and position of Queen was to be given to another. Some may say what is the difference. Well, the difference is one is divorce and the other is separation, one is sinful and the other is not.
Est 1:19 If it please the king, let there go a royal commandment from him, and let it be written among the laws of the Persians and the Medes, that it be not altered, That Vashti come no more before king Ahasuerus; and let the king give her royal estate unto another that is better than she.
Est 1:20 And when the king's decree which he shall make shall be published throughout all his empire, (for it is great,) all the wives shall give to their husbands honor, both to great and small.
Est 1:21 And the saying pleased the king and the princes; and the king did according to the word of Memucan:

So because the King did not divorce Queen Vashti there was no sin in marrying Esther and making her the Queen of Persia.

The truth about Queen Esther of Persia