How has Desdemona and Othello's relationship changed since the beginning of the play?

Desdemona is a pretty static character through the play. Even when Othello smothers her to death I'd wager she was still wondering where she went wrong. From a feminist perspective poor Desdemona was pretty much a doormat. She was strong but only in her unflinching ability to support her husband. To her father Desdemona professes her love and undying loyalty, "And so much duty as my mother showed to you preferring you before her father. So much I challenge that I may profess, due to the moor my Lord." Othello, on the other hand, is more dynamic except in a manic sort of way. Early in the play Othello worships Desdemona and eve foreshadows himself becoming Mr. Crazy should his love ever change, "But I do love thee! and when I love thee not, Chaos is come again." Othello then takes the fast train to paranoid town. Sure he loves Desdemona as far as he has branded her his. When his ownership comes into question, his love and very identity become a violent tempest. It's the old Madonna/hoar syndrome that many of Shakespeare's leading men had. Othello's was particularly bad. He needed to worship Desdemona. When he feels in danger of becoming the dreaded cuckold, he snaps and Desdemona comes tumbling down from her alter.