In a study published last year (4/29/14) from researchers at the University of Wisconsin-Madison, including Dr. Richard J. Davidson, stress levels of married couples were shown to influence each partner's happiness. Researchers looked at how often spouses felt let down or criticized by their partners and found that those in unsupportive marriages had more trouble sustaining happiness. Dr. John Gottman has discussed feeling criticized by one's partner in his research on marriage over several decades. Dr. Gottman has found that criticizing one's spouse is predictive (along with other variables) of divorce. Over time if our spouse has continued to criticize us we may develop a general mistrust of their intentions. For example if they actually say something nice we may have become conditioned to disregard this positive comment or hear some "hidden" negative meaning in it. The only way to prevent this is to fully repair instances where one has hurt one's partner. While this sounds cumbersome to some, learning to quickly and effectively repair is a skill and can be learned. Relationship skills are like any skills and once mastered can be performed easily and fluidly, like learning a foreign language or new sport. So even if it takes effort and practice early on this repairing becomes faster and easier but continues to yield huge results.
If you or your spouse is depressed there are some studies that support the idea that couples therapy may help more than other treatments. In a study done in 2012 Dessaullesa, Johnsona, and Dentonb found that when one spouse is depressed and the relationship is also under stress couples therapy may outperform antidepressants. Leff et al. in the British Journal of Psychiatry (2000) found that partner's depression improved after either couples therapy or antidepressant medication. However the couples therapy group continued to show those gains at a one year follow up while those treated with medication did not.
In summary if you find yourself depressed, or if your partner is depressed, and your relationship could use some attention as well you may get more benefit from couples therapy than medication or other interventions like individual therapy. It's important to remember that depression has very serious health consequences as well as emotional pain and should be treated or it can worsen.
With warm wishes,