Matthew 1:19 (BSB)

Because Joseph her husband was a righteous man and was unwilling to disgrace her publicly, he resolved to divorce her quietly.

From Matthew 1. Also in the ESV.

Commentary on Matthew 1:19

• John Calvin (Reformed), Calvin's Commentaries on Matthew 1:19: 19. As he was a just man Some commentators explain this to mean, that Joseph, because he was a just man, determined to spare his wife: “Que Joseph a voulu pardonner a sa femme, et couvrir la faute, d'autant qu'il estoit juste.” — “That Joseph intended to forgive his wife, and conceal her offense, because he was just.” taking justice to be only another name...
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Matthew 1:18-25: The mystery of Christ's incarnation is to be adored, not pried into. If we know not the way of the Spirit in the formation of common persons, nor how the bones are formed in the womb of any one that is with child (Ecc 11:5), much less do we know how the blessed Jesus was formed in the womb of the blessed virgin.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Matthew 1:19: Then Joseph her husband,.... To whom she had been betrothed, and who was her husband, and she his wife according to the Jewish law, Deu 22:23 though not yet come together, being a just man, observant of the law of God, particularly that which respected adultery, being wholly good and chaste, like the Patriarch of the same name; a character just the reverse of that...
• Albert Barnes (Presbyterian), Barnes' New Testament Notes on Matthew 1:19: Verse 19. Her husband. The word in the original does not imply that they were married. It means here the man to whom she was espoused. A just man. Justice consists in rendering to every man his own. Yet this is evidently not the character intended to be given here of Joseph.