What is the antonym of "dependent"? [duplicate]
Perhaps the term provider or the phrase principal provider conveys the relationship.
SUPPLEMENT: I think JLG is right that this is a duplicate (and others have suggested what I propose).
Depending on the circumstance, if A is the dependant of B, then B may be the guardian of A. As tchris noted, this would apply for a parent-child relationship, but it does not fit when referring to spouses.