There are no happy marriages in Hard Times. In Stephen's case, it focuses instead on a missed opportunity for true companionship. In the case of the Gradgrinds, you've got an entirely intellectually unequal match where spouses are indifferent to each other. Then there's a loveless disaster where husband and wife grow to hate each other in the case of Louisa and Bounderby. The only happy unions are mythic, have occurred in the past, or are just barely implied, as in the case of the Jupes or Sissy and her eventual family.
The novel demonstrates the conflict between two ways of thinking about marriage: as a romantic partnership versus as primarily financial arrangement. It argues that in neither case is it a relationship that is meant to last forever.