Walter and Ruth are not happy. They have a troubled relationship with tension stemming from at least two sources.
Walter feels that he is wasting his life as a chauffeur. His job offers him no dignity.
He works as a chauffeur, a job he finds unsatisfying on a number of levels but most particularly because he does not desire to be anyone's servant.
In this diminutive self-perception, Walter becomes resentful of Ruth, projecting his self-contempt onto her. There is reason to intepret this negativity as a resentment that is actually directed inward. Walter feels that he has failed his wife and his son.
Ruth does not agree with Walter's view of himself. This difference in perspective creates some of the verbal conflict from the play's first act.
The pressures of poverty that lead Walter to feel like a failure lead Ruth to attempt to focus on the bare, positive facts: at least the family is together. They have each other.
She clearly loves her husband and family but also clearly feels the stress of poverty.
When Ruth discovers that she is pregnant, a new conflict emerges. Another child will be a financial burden on the family and there is already too little space for the family as it is now in the cramped apartment.
Walter, in his self-loathing, is desparate to find a way to express his true potential as a man, a husband and human being. The pregnancy looks like a challenge more than a blessing. As their relationship suffers, Ruth begins to feel this way too.