In a relationship chart the composite Moon describes the emotional coloration and requirements of the union, and the 8th house rules the parts of life that no one wants to openly talk about. The Moon represents our need for security, refuge and retreat, and it isn’t always comfortable in the 8th house.
The relationship is left sensitive to the feelings of being unsafe, threatened, and provoked, and also when you care about someone you love, you learn all of each others strengths and weaknesses and then one is fully armed to do the most damage. Whilst this is an incredibly bonding Moon the feeling are powerful and there could be painful lessons about letting go. Furthermore, the couple might have to undergo emotional crisis and enormous change in their personal life. Almost everything in the couple’s world triggers thesepowerful emotions.
The water houses also have something to say about the psychological family inheritance from both sides of the family. The emotional side of this relationship is hidden from other people, and represents the most sensitive and vulnerable area in the couple's life. The 8th house rules abuses of all kinds, secrets, and transformational healing. It’s here where the couple have emotional access to the hidden depths of relating and it also puts the emotional focus on the survival of the relationship itself.
With the composite Moon in the eighth house, nothing of a psychologically edgy nature is going to remain buried for long between these two. Their relationship seems to to have a defective repressive mechanism. That can beautiful, in that it promotes truthfulness, transparency and a kind of "nakedness" between them. Naturally it can also prove volatile. Jealousy, anger, possessiveness, insecurity-whatever they don't want to see in themselves---is quickly open. Skymates, Vol. II: The Composite Chart (Volume 2)
The 8th house also deals with death, sexuality, psychology, shared resources, taxes and legacies. A really good way to understand how the composite Moon in the 8th house is operating when it is below the surface level of life is to observe what happens when a transit aspects the composite Moon. Pay particular attention to the heavy transiting planets – Jupiter, Saturn, Uranus, Neptune, and Pluto that is when the couple will get the best understanding of how this Moon is operating.
The composite Moon in the 8th house can create an emotional storm, and if it is not handled well, and it may create deep seated, and underlying resentment. The emotional side of the relationship has the ability to re-new itself and transform deep rooted problems in the union. However, the couple may encounter some difficult emotional encounters together and feelings of emotional betrayal, and a kind of emotional naked feeling one is truly stripped bare. Plus the emotions run along the volatile, angry, jealous and possessive kind.
The couple can move into greater depths of relating. However, if the two of you manage to weather the storm it can transform the union and it be incredibly healing, but only once the couple understands the true emotional depths which the relationship requires.