Getting to spend your life with one person is one of the luckiest things imaginable. When my husband and I were planning our wedding many years ago, I got asked a lot of questions. While everyone wanted to know about the color scheme and wedding venue, the one thing I got asked a surprising amount was: "How did you know he was 'the one'?" The answer, of course, can be pretty long-winded and personal. Even though we might love many people in our lifetime, there might also be one person who excites you and who you want to be with for the rest of your life. Finding "the one" is special. Consider these traits of a relationship that can let you know you have found that one person who will make you smile until you're old and gray.