Here's a summary of some of the more important themes of a natal Venus-Neptune aspect:
Idealistic, future-looking, longs to be enchanted. Wants things perfect. Can become jaded, disillusioned, and cynical from repeated hurtful betrayals. Emotions run strong. Most sees beauty in people and things, thus has blind spots (especially in romance). Trusting, naturally confident of others’ goodness (poor discrimination in selecting friends). Good-hearted, caretakes others, devoted friends, romantic, humanitarian. Natural people-readers (when not personally involved), natural psychologists.
Here is an interpretation of Neptune transiting Venus:
The progression can be expected to be a blend of the two of these.Romantic idealism fills you. Your temperament leans toward the emotional and sentimental. The beautiful in people and things catches (and holds) your attention, with all the advantages and problems that can bring. Positively, your heightened esthetic sense is attuned to the world's beauty, fueling your soul with wonders if only you pay attention. Imagery captivates. You are open to fresh levels of sensual delight. More of a problem is a sometimes undue naïve confidence in people's innate goodness, wearing blinders to their faults, particularly in romance (possible romantic disappointment). You pursue an unreachable love object (e.g., involvement with someone already romantically committed; spiritual devotion, seeking a "wedding with God;" having an exalted ideal for a lover that cannot be met, etc.). Yet, in your quest is pleasure. You are more vulnerable to disappointment and more emotional; but the basic tone of the time is enjoyable, even Utopian.