In Desiree's Baby, the couple is Mr. & Mrs. Aubigny, Armond and Desiree, Mr. & Mrs. Mallard are from Kate Chopin's "The Story of an Hour."
For the Aubignys, I would agree that he loved her in the beginning and then betrayed her, rejected her because of a belief that he held that she has African ancestry, as exhibited by the child they had together who appears to have 1/4 African ancestry.
It is a case of altered perception, as if Armond, loved the idea of Desiree, not the real woman, because Desiree, after the child is born and displays 1/4 African ancestry, is the same loving, kind woman, Armond cannot accept his wife because he feels that he has been cheated, even though he knew that Desiree's heritage was unknown.
Armond is revealed to be a racist, a liar, a man of no morals. He feels superior to Desiree, after the child is born, feeling as if he should be able to return this damaged possession. Armond views everything in his life as possessions, his wife, his child, he does not really love anyone but himself.
Armond, who marries Desiree with the acceptance of her unknown heritage, claiming that he did not care about the fact that she did not know her real parents, that he, in fact, would give her a new name, apparently was a lie. He did not really love Desiree, he turns out to be a fraud.
Also Desiree, a mother, really loves her child, as her mother, adopted mother, really loves her, Armond, the man that Desiree was so thrilled to marry and from whom she craved acceptance, rejects her because he believes that she has African ancestry, so like so many marriages, Armond finds out something about his wife after the fact, that alters his perception of her, therefore, he rejects her completely.
Desiree is so insecure about her unknown heritage, having the rug pulled out from under her with the birth of the child and his African ancestry, she feels so responsible for this, and her love for Armond is so great, she feels such shame about her heritage that she doesn't just walk away, she wants to wipe out her existence so that Armond won't have to see her or deal with the child.
She can't bear the thought of her son being rejected by his father, so she walks into the swamp committing both murder and suicide to relieve Armond of the terrible burden that she has placed upon his life.
Armond is the real fraud, it is interesting that everything he accuses Desiree of, he is guilty of, it is he who has contributed the African ancestry, not Desiree.