Moon in the 7th house synastry means their Moon falls in your 7th house: where their feelings land in your life. What it feels like from both sides, the gift, the shadow, and how to find your overlays.
Moon in the 7th house synastry means their Moon falls in your 7th house: partnership, marriage, the mirror, and the person you commit to one to one. Their feelings land squarely on the question of "us". They want to be your partner, not your friend or your fling, and they tend to feel that pull early.
Their Moon in your 7th house
They start thinking in pairs before you do. Plans get made for two, a plus-one is assumed, and "what are we" surfaces sooner than usual. For you, this can be a relief if you were ready and a pressure if you were not, because their moods rise and fall with the state of the relationship itself: a good week between you and they are radiant, a distant week and they wilt. For them, you look like the partner they have been describing to friends for years, and being chosen by you is the comfort they are after. The classic pattern is that each of you sees your own emotional habits reflected back, sometimes uncomfortably. Fights tend to be about fairness and reciprocity. Commitment, a ring, a lease, an introduction to parents, carries unusual emotional weight here.
The gift
Being wanted as a partner, plainly and without games, is a rare thing to be handed. You get someone who shows up for the relationship as a relationship: who negotiates, compromises, remembers what you agreed. They get to be met, because this house is yours too and you tend to bring your best relational self to it. Couples with this overlay often become good at repair, the apology and the conversation after the fight, which matters more over time than avoiding fights altogether.
The shadow
When their comfort depends on the relationship being good, every rough patch becomes a threat. They may push for definitions, exclusivity, and reassurance faster than you can honestly give them, and you may feel your independence shrinking to keep their mood steady. On your side, it is tempting to let them carry all the feeling in the relationship while you play the reasonable one. Projection runs both ways: you can each mistake the mirror for the person.
Working with it
Decide the pace of commitment together, out loud, rather than letting their anxiety or your hesitation set it silently. When they need reassurance, give a specific one, "I am glad I picked you," instead of a vague "we are fine." Keep your own friends and your own evenings so that the partnership has two whole people in it. After a fight, name your part before you name theirs; this overlay rewards fairness more than winning.