ANSWER: If the man divorced his first wife for the cause of fornication and was scripturally joined in marriage to the second wife, he cannot! If he did, he would be sinning by divorcing the second wife (to whom he was joined by God) without scriptural cause and by committing adultery with his ex-wife (Matthew19:3-9)! If he divorced his first wife without scriptural cause, he sinned, and then compounded the sin by committing adultery with his second partner in a marriage not approved of by God. In this case, scripture demands that he repent by leaving the second partner and returning to the first. If it is the case that the first wife has “a friend” (I assume this means that unlawful sex is taking place), she and the “friend” are committing the sin of adultery. The first wife and the “friend” need to repent and discontinue the relationship or they are both going to be lost eternally. If there was not scriptural cause for the original divorce, the first wife and the husband need to reunite. If circumstances prohibit a reunion, then both the husband and the wife must remain single and celibate (Matthew 19:9).