Since the person you marry makes a huge difference in your happiness and even your career and earning power (but possibly not in the way that you might think), maintaining a great relationship is incredibly important.

But that's hard to do if one of your commutes is relatively long; according to at least one study, if one spouse commutes longer than 45 minutes, you are 40 percent more likely to get divorced.

But that doesn't mean those relationships are doomed. If you've already spent five years or more commuting more than 45 minutes, then you're only 1 percent more likely to get divorced than couples with short commutes. In all likelihood, that's because you've worked through the practical and emotional issues involved. (More on that in a minute.)

Plus, if one of you had a long commute before you started your relationship, then you're also a lot less likely to get divorced than husbands or wives who start a long commute later in their relationship. (More to come on that too.)

Why does the divorce rate climb steeply when a long commute is involved? In this post, HubSpot co-founder Dharmesh Shah suggests several possible reasons:

1. One partner may have to take a job closer to home, especially if they have kids.

Say a wife takes a job with a long commute. Limiting her husband's job prospects to a smaller geographic area may mean he has a less satisfying career and is forced to assume an even bigger role in raising the kids and taking care of the home. For some people that could be a real problem.

Of course, it doesn't have to be; my commute is two flights of stairs, so it's natural for me to take on more household duties. It all depends on how you and your spouse decide to share responsibilities--and how you feel about sharing those responsibilities.

2. Time is the glue that holds relationships together.

Long commutes take away time--from significant others and from kids--that is lost forever.

3. The money is rarely worth it.

Say you get a 20 percent bump in salary, but you have to drive an extra hour. According to another study, economists determined a 40 percent increase in pay is necessary to make an additional hour of commuting time pay off in terms of personal satisfaction and fulfillment.

In simple terms, a couple of dollars an hour more won't make you happy if you have to drive an extra hour every day to earn it.

4. Long commutes can be stressful, especially when heavy traffic and frequent delays are involved.

It's hard to walk in the door happy when you've played freeway bumper cars for an hour.

But then again, for three years I commuted two hours each way, but the actual drive was a breeze (and I got to listen to a ton of books on tape). But I can't imagine commuting to and from Washington, D.C., every day. Ugh.

5. The guilt could eventually get to you.

When your spouse and kids miss you, it's easy to feel the tradeoff between time and money is selfish or in some way self-serving. So you start to act differently, either defensively or indulgently (or both). You make decisions you might not have made. You say things you might not have said.

Of course, you might not have a choice about the commute. Maybe, because of where you live and the career you've chosen, a long commute is your only option. In that case, it's best to make the most of it and do what you can to make the rest of the time at home count.

But if you do have a choice, think hard about the tradeoff between time and money (or title or prestige or whatever the lure of a new opportunity).

Or better yet, find ways to make it work.

My wife commutes two hours each way to her job, but through creative scheduling, she only works a few days a week. (Granted, they're 24-hour days.) And she teaches at a university 3.5 hours away, but one of the courses is online. And we have a house nearby, which makes it easier.

For us the tradeoff works, because while she is in the car more, she's also at home more. That also works for us because I have no commute: Whenever she's home, I'm home. And I can creatively schedule my time--and make sure all the household stuff like cleaning, laundry, bills, etc., is taken care of--so we can take advantage of the time she's home.

Plus, we're used to long commutes and spending time apart. When we first met, she was about to take a job in NYC. We dated long distance for a while, got married, and at first had a house in New Jersey and one in Virginia. After a year, she took a job in Pennsylvania, which meant we still had two houses.

When we finally ended up in one house, she almost immediately went back to school, and that meant a 1.5-hour drive each way, so add it all up and, yeah, we know how to deal with long commutes and multiday separations. While it's certainly unusual, it works for us. We made all those decisions together; I fully support what she does, and she fully supports what I do, so there's no resentment or festering emotions.

And possibly, that's the biggest takeaway. No two relationships have to be the same. What works for your relationship might not work for mine.

What matters is that your relationship works for you and your spouse.

Still, don't ignore the impact of a long commute on your relationship--or, for many entrepreneurs, significant travel.

If you're struggling to decide whether an opportunity makes sense, here's one way to look at it: You sometimes might regret the opportunity that slipped away, but you will always regret the time with your loved ones you let slip away.

What do you think? How do you deal with the effects of long commutes or frequent travel on your relationship?