The second time Jesus crosses the line and mentions male sexuality is in Matthew 5:31-32.
“It was also said, ‘Whoever divorces his wife, let him give her a certificate of divorce.’ But I say to you that everyone who divorces his wife, except on the ground of sexual immorality, makes her commit adultery, and whoever marries a divorced woman commits adultery.”
In Matthew 19:3-9, Jesus addresses the same issue, and with more details.
Men are prone to desire a wife that will satisfy him sexually.
Thus Jesus is saying a husband cannot divorce his wife unless she has been sexually immoral. Why does Jesus say this? Very, very few women are seeking a divorce on the grounds that her husband does not satisfy her sexually. Married women may not be sexually content, but very, very few of them are looking for plan B on the basis of her sex life.
This is a male issue, not a female issue. The sexes are different in this way. Thus Jesus reigns us men in, and says, “Stay married. If your wife crosses the sexual immorality line your first response to to forgive her and work to repair your marriage. If she refuses, and continues to refuse to work on her marriage, then a husband may divorce his wife.
There is no command for a man to divorce his wife.
There is only a command that a divorce can happen, if it absolutely must be because of sexual immorality.
Needed Endnote: There are other valid reasons for a husband and wife to separate.
The Men's Bible Reading Idea 