The only Air Nomads known to have married are Aang and Tenzin. It is unknown whether the Air Nomads before the Hundred Year War practiced marriage at all - parents gave up their children to be raised by the monks or sisters as a way of getting rid of earthly attachments, so the Air Nomads may just have a child as a way of continuing the Air Nomad lineage, and not for the purpose of a family and marriage.