Composite Neptune in the sixth house indicates that the two of you may have a very high ideal of service to others, or else you may be unclear about what you are supposed to do as a couple.
Work, or just plain getting things done, becomes kind of a philosophical ideal for a couple with this placement. But remember that every relationship must provide to some extent for the individuals' legitimate demands for self- expression.
If the two of you become too wrapped up in the ideal of service, either to each other or to others, it can lead to a very subtle form of resentment, in which one or both of you plays the martyr. If you are sincere about your ideal of service, fine, but give yourselves room to get what you need in the relationship als