When you're an introvert, having friends takes on a different meaning. My parents noticed early on that I had very few friends, but the friendships I did have were solid. Now I'm a 35-year-old married dad with two girls and nothing has changed.

For the last 20 years, outside of my wife, I've really only had one good friend. My friend and I met in 9th grade during football practice, and the rest is history. He was my roommate in college, the best man at my wedding, and even though we now live 3,700 miles apart, he still reaches out the moment he learns that something isn't going well with my life.

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My wife is the only other person who has been able to insert herself into my life as a friend and I now consider her to be my best friend.

I don't say "I love you" to just anyone, and I sure don't make just anyone my best friend. Over the last 15 years, I've come across maybe five people I would consider spending time with outside of work. So obviously, my wife has a lot of time to be my only friend and my introverted self doesn't want/need to find any other pals to help fill that void.

My wife couldn't be more different. She makes friends with ease and has lots of 'em; her friendships are very important to her. They serve as a support system in her life and the more support she has, the better she feels about herself.

She has friends she has met online, friends she met through family, and even friends she's met on vacation. What we don't have are many couple friends and that's my fault. My inability to make friends with the spouses of her friends has caused tension and was one of the reasons she decided at one point that she wanted a break from our marriage.

Up until recently, my wife didn't bother to understand how an introverted brain works.

She has since read books about introverts and has asked me more about my experience, but she'll never fully grasp why I'm an introvert. She won't ever fully understand my reluctance to let anyone into my world. She won't ever figure out why I wouldn't want a ton of friends in my life the same way she has in her life.

Likewise, I don't understand why my wife allows just anyone into her life and opens herself up to betrayal and disappointment by having so many casual friends. I certainly don't understand the way she classifies her friends in some sort of tier arrangement.

But what I don't understand the most is why she doesn't classify me as as her best friend.

When my wife tried to explain to me that she didn't consider me to be her best friend, she drew a chart to explain how she classifies the people in her life in a tier arrangement like this:

In her words: "I will always be able to do anything I do with my friends with you, whether you enjoy it or not is a different story. However, there are things that I do with you that I would never do with any of my friends (or anyone else) no matter how close we were."

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Although I don't think we'll ever fully understand each other, over the course of 13 years of marriage, we've learned that fixing each other doesn't work as well as trying to meet in the middle and work with each other through whatever issues seem to come between us.

As a result, I've tried to make more of an effort to appear friendlier when we meet with other couples, and she tries to help facilitate those friendships in a more introverted manner.

We've also come to realize that the more we understand our differences, the more we realize how much it benefits our marriage. For instance, because I don't have many friends, I don't go out very often, which means I’m home ... a lot.  And because I'm home a lot, I can take care of our kids while my wife spends quality time with her friends.

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This arrangement allows us both to spend time in our comfort zones; it makes us happy. And there's one thing that is as sure in marriage, as death and taxes are in real life: a happy wife truly makes for a happy life.

Cody Mullins is a contributor to YourTango.