My mother has lost two husbands whom she loved very much. The first died in a car accident in his 20's. The second (my father) died from a brain tumor in his late 50's (after 30 years of marriage). I can't imagine going through the pain of losing two spouses in a lifetime, but nonetheless she is a happy woman to this day.
When you get towards the end of your life, I believe you reap what you sow. My mother is only 60 years old (not near the end of her life hopefully) but she has always been a very loving and giving person with a great personality. Because of that, she has a lot of family, mine included, who love to do things with her and spend time with her. She also has a lot of grandchildren that she enjoys getting to see, and likewise, she is their favorite person in the whole world, believe me!
Through living such a full life and being such a warm and generous person, I know that her entire world didn't revolve around my father, and I think that made coping with his death easier. She still has good support and many beautiful people and things in her life.
But was it easy for her? No, not at all. I think it's safe to say that she was probably "depressed" for the first year or two from the grief. I know from my own experience that it has gotten easier with time.
So what does all of this mean as far as an answer to your question goes?
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Your life can have more meaning than just this "one person."
You and your relationships with others can continue to inspire other people long after you or your spouse passes on.
I carry this poem in my wallet, because it's how I want to live my life, even though I'm sure I fall short on a regular basis:
"Success" by Bessie Stanley
He has achieved success who has lived well, laughed often and loved much;
who has gained the respect of intelligent men and the love of little children;
who has filled his niche and accomplished his task;
who has left the world better than he found it, whether by an improved poppy, a perfect poem, or a rescued soul;
who has never lacked appreciation of earth’s beauty or failed to express it;
who has always looked for the best in others and given them the best he had; whose life was an inspiration; whose memory a benediction.