You might like to look at Act IV scene 2 of this great play, which is of course when Othello challenges Desdemona directly with her supposed adultery. In their conversation we see how his former enamoured state has been eaten up by jealousy, as he refers to her in less-than-flattering terms. Consider how he describes her in the following description:
O thou weed
Who art so lovely fair and smell'st so sweet
That the sense aches at thee, would thou hadst ne'er been born!
He goes on to call her an "Impudent strumpet" and then calls her "that cunning whore of Venice." The use of strong language and Othello's open denunciation of Desdemona's character clearly indicates the way that his love and joy in his marriage and relationship with Desdemona has been gradually eaten up thanks to the stratagems of Iago and Othello's own pride and sense of jealousy.