This is a really interesting distinction. From Unforbidden Pleasures, by Adam Phillips, pg 85:
Ambivalence does not, in the Freudian story, mean mixed feelings, it means opposing feelings. ‘Ambivalence has to be distinguished from having mixed feelings about someone,’ Charles Rycroft writes, in his appropriately entitled A Critical Dictionary of Psychoanalysis (as though an ‘Uncritical’ dictionary would be somehow simple- minded):
“It refers to an underlying emotional attitude in which the contradictory attitudes derive from a common source and are interdependent, whereas mixed feelings may be based on a realistic assessment of the imperfect nature of the object.”
Love and hate – a too simple, or too familiar, vocabulary, and so never quite the right names for what we might want to say – are the common source, the elemental feelings with which we apprehend the world; and they are interdependent in the sense that you can’t have one without the other, and that they mutually inform each other. The way we hate people depends on the way we love them, and vice versa. And given that these contradictory feelings are our ‘common source’ they enter into everything we do. They are the medium in which we do everything. We are ambivalent, in Freud’s view, about anything and everything that matters to us; indeed, ambivalence is the way we recognize that someone or something has become significant to us.