Having someone to talk to and help you work through difficult times is a major benefit of a long-term relationship. A girlfriend can provide emotional support and companionship, which may help reduce stress levels. According to a University of Chicago study, people in committed relationships produce lower levels of the stress hormone cortisol. The study, published in the journal "Stress," in September 2010, suggests that single people are more susceptible to psychological stress than are those in long-term relationships.