Matthew 5:28 and marriage
With Matthew 5:28 in mind, is it a sin to lust sexually after your spouse (if you are married)?
God designed sexual relations for the marriage bond (Hebrews 13:4). Jesus’ words in the Sermon on the Mount speak of sinful thoughts toward someone who is not part of the marriage bond.
With your question in mind, it could happen that a person’s thoughts of his/her spouse could distort God’s design for marriage, in that the person looks upon the spouse as a sex object. 1 Corinthians 7 tells husbands and wives how to view each other and themselves when it comes to their sexual lives.