Spouses are assigned to most adults, but in Chapter 13 we learn that the Giver’s now lives with the childless adults.
In Jonas’s community, families are created very differently. The community has embraced Sameness wholeheartedly, which means that there are strict rules for everything and almost all decisions are made for the citizens of the community. The family unit is created when two spouses are matched, and then children are added one at a time from the fifty born each year through genetic engineering.
Not everyone in the community has a spouse. Jonas comments that some people are segregated from normal community functions.
Most of the people on the night crew had not even been given spouses because they lacked, somehow, the essential capacity to connect to others, which was required for the creation of a family unit. (Ch. 1)
The family unit is basically designed for the raising of children. This is why there are only two children, a boy and a girl, and the spouses are matched based on compatible personalities.
Even the Matching of Spouses was given such weighty consideration that sometimes an adult who applied to receive a spouse waited months or even years before a Match was approved and announced. All of the factors—disposition, energy level, intelligence, and interests—had to correspond and to interact perfectly. (Ch. 6)
The idea is to maintain a stable community by having stable family units. As soon as the children are grown, the family unit disbands. The children go their way, and the parents go theirs. They have basically no contact after that. Adults with no children live with the Childless Adults until they become old enough to enter the House of the Old, and then they are eventually released.
After Jonas begins his training, the Giver explains to him that having a spouse when you are the Receiver of Memory is a little difficult. He had a spouse, but since their children are grown (well, one is presumably grown, but the other is dead), she lives with the Childless Adults and he has his own special dwelling.
"You'll be able to apply for a spouse, Jonas, if you want to. I'll warn you, though, that it will be difficult. Your living arrangements will have to be different from those of most family units, because the books are forbidden to citizens. You and I are the only ones with access to the books." (Ch. 13)
The Giver explains that there are many aspects of the Receiver’s life that a spouse cannot take part in or understand. Being forbidden to access books is just one part of it. The Receiver knows everything about the history of the community, while all other citizens just assume that things have always been as they are. Memories allow a person to have emotions and feelings, which no one else in the community has.
There is a reason the Giver doesn’t think Jonas should have a family unit. The Giver’s family allowed him to have a daughter who had the same gift he did. Rosemary was selected to be trained as the next Receiver of Memory and the Giver found it difficult to train her properly because he did not want to transmit pain to her. Rosemary’s training resulted in her death, because she was so horrified by what she saw and what she learned about her community that she requested release.