There are many obstacles in this deeply unhappy relationship. For one thing, Reverend Bentley is either unwilling or unable to give his wife the kind of attention and affection that she so desperately craves. This leads to Mrs. Bentley finding comfort in the friendship of Paul Kirby, although their relationship doesn't go any deeper than that.
The Reverend's lack of affection of his wife leads to Mrs. Bentley to conclude that perhaps he's been showing affection towards another woman. When the Bentleys' housekeeper, Judith, falls pregnant, Mr. Bentley immediately jumps to the conclusion that Judith is carrying her husband's child. Inevitably, this places an additional strain on an already fractured marriage.
The main obstacle in Mr. Bentley's relationship with her husband seems to be the lack of children in the household. It's notable that when the Bentleys look after a young Catholic boy named Steve their relationship dramatically improves. By the same token, their marriage experiences difficulties once more when Steve is adopted by Catholic priests.
It would seem, then, that what the Bentleys really need to bring them together and renew their broken bonds of affection is a child. And a little bundle of joy duly arrives in the shape of Judith's baby. As Judith has tragically passed away, her child will now be brought up by the Bentleys, who can now look forward to a much better, happier relationship.