Jupiter in Synastry Chart Overlays...

The planet without limits. 
Jupiter can make you feel invincible!
Jupiter is fun, expansive, lively, 
candid and intellectual.
Considered by many to be the most beneficial planet in astrology, Jupiter lightens a house. It makes things seem easier, less crucial and less serious. It can intellectualize a situation that would otherwise drag more emotional people into a depression. Jupiter makes things come naturally and easily in the house blessed with its presence. 

This ease of functioning stems largely from Jupiter's expansive nature. Jupiter doesn't believe in limits, so when things are good, they can be really good! Jupiter in synastry chart overlays has the same effect.
In the first house of a synastry chart overlay, Jupiter can perform some amazing magic. Your partner's Jupiter in your first house can make you feel larger than life. Confidence will bloom, making you feel more powerful and attractive. In the fifth and seventh houses, the effect is similar in that Jupiter accentuates the positive and dismisses the negative. Fun and flirting flow easily, boosting attraction levels. Your partner's Jupiter is in the second, sixth, or tenth house of your synastry chart overlay. It can help release your stress in these houses of day-to-day issues of money and work. 
Your partner's Jupiter in your eighth house can make intimacy, commitment, and the give and take in the relationship easier by bringing its unbiased, philosophical outlook and generosity to the house. Jupiter fits in nicely in both the third and ninth houses. Your mate's Jupiter in either of these houses can expand your philosophical, religious, or political views. It may inspire you to learn more about new topics, travel more and to communicate more freely with your mate. In the fourth house, your partners' Jupiter can lead to a large family or, at the very least, make family life an easy experience. Your mate's Jupiter in your eleventh house will lend its easy-going ways to your social and community life, assisting in such things as social networking. A twelfth house Jupiter from your partner can help to open normally unconscious issues and bring them to light, relieving the burden of hidden, misunderstood feelings which can loom in relationships. Jupiter has a lot of good to offer, and Jupiter's gifts are meant to be enjoyed, but be careful. All of Jupiter's wonderful gifts also have the potential for breading disaster if certain warnings aren't heeded. Like Icarus who flew too close to the sun, 
Jupiter can overdo things and ignore rules and limitations. This, combined with its undying optimism, can lead to carelessness and to taking things for granted, or ignoring things completely. In a synastry chart overlay, this can be a disaster. Expecting your mate to take everything lightly or ignore the matters of any house in which it falls, does not go over well with many people. Especially if that thing is going too far with flirting with other people, or going on all night adventures without them. Even being too candid or intellectualizing a problem that really deserves a little tender emotional support can come off as insulting and cavalier. Another pitfall of Jupiter is expecting people to give limitlessly in houses like the second 
and eighth. Or in houses like the sixth and tenth, Jupiter can be so expansive, limitless, and fun that it sometimes overlooks things in life, like chores and career, that may be boring and serious but are necessary and important. Enjoy that limitless, unbiased feeling of freedom that Jupiter brings to a house, and remember to cherish and value these gifts. Jupiter is also wise and can make a fool of those who waste its gifts. Use its wisdom rather than wasting it, and enjoy!