Leo in the Navamsa brings the Sun's fixed-fire authority to the marriage house, and the union it describes tends to carry a certain visible dignity — partners who present well together and expect the relationship itself to be a source of pride rather than quiet compromise.
A spouse indicated here is classically read as confident and warm, often with real leadership qualities of their own, drawn to a partner who can meet them as an equal rather than defer to them. Genuine mutual respect, once established, tends to produce real loyalty and generosity within the marriage.
The Sun's own singularity is the classical caution: two strong wills each expecting to be the center can produce real friction, and the same pride that makes this placement dignified can make it slow to apologize. The lesson is directing that solar warmth outward, toward the partnership, rather than holding it as a personal claim to being right.