Composite Venus in 12th house:

Venus is the planet of love and affection but when located in the 12th house you may tend to keep these feelings hidden or else you may not be able to express them. The people in your environment may not be aware that you have feelings for each other. Venus in the 12th house is an indication of a secret relationship. This is a wonderful position of Venus for overcoming any ego differences within your relationship as it allows you to give way to the other without feeling vulnerable. You will be able to work together as a unit rather than as individuals, thus adding strength and support to your relationship.

This interpretation is from the Relationship Composite Report.

Do you and your partner have Venus in the 12th house in your composite chart? What's it like?