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.

A girlfriend can have a positive impact on your health, according to an April 2012 study from the University of Minnesota Medical School. Researchers found that if someone makes healthy eating and exercise a priority, her long-term partner is more likely to do the same. If your girlfriend is whipping up tasty, nutritious meals for you both and encouraging you to get off the sofa and go out for a run, you are going to reap the benefits, both mentally and physically.

Having a girlfriend may provide a secure base from which the confidence to make important decisions and tackle life's problems develops, says Joseph Dragun, Ph.D., psychologist and founder of the Relationship Center of Michigan, in "Falling in Love is Not Enough." Embracing challenges and overcoming obstacles becomes easier when you have the security of a close, committed relationship, Dragun adds.

You may be more likely to trust and see the good in other people when you have a girlfriend, Dragun says. Knowing that she loves you and cares about you boosts your self-esteem, which makes you feel better about yourself. This is then reflected on your view of others in your life. According to Dragun, people who are in close, loving relationships tend to be more successful and are more satisfied in their careers. Achieving your goals may be easier and more enjoyable when you're on a team of two.