Aspects of malefic planets (the Sun, Mars, Saturn, Rahu, and Ketu and the lords of the sixth, eighth and twelfth) to the seventh house or its ruler tend to cause separation or divorce. The Sun will make us too individualistic or dominating. Saturn will make us too contrary, solitary or fearful. The aspect of Mars can cause conflict or sorrow, and is a factor in Kuja Dosha.
Rahu will give us unrealistic expectations and confusion of motivation. Ketu will make us defensive and contracted. The lord of the twelfth will cause us to negate relationship. The lord of the eighth or sixth houses can also be difficult here, not only for relationship but for health.
On the other hand, aspects of benefics boost up the seventh house and its effects. Best on the seventh or its lord is the aspect of a benefic Jupiter. It can guarantee happiness in relationship. It creates understanding of the partner and good will in relationship. It is particularly strong if Jupiter is also ruler of the seventh. The aspect of the Moon is generally good unless the Moon is waning and afflicted. The Moon gives a capacity to communicate and sensitivity of feeling, a general openness and sharing.
The aspect of Venus to the seventh is helpful for giving affection and for making the individual attractive. The aspect of Mercury increases communication but does not guarantee lasting contacts.
The aspect of the lord of the seventh to the seventh is usually helpful, unless it is a malefic. But even this is not always good if it comes from the first house, which can show the seventh lord limited to the sphere of the self (first house).