22 years, 11 kids, and we still have a lot of "magic". I feel there is a lot more "magic" now that we had when we were first married. I like her more now than I did then.
We all run consistently, myself, wife and kids - even the young ones as soon as they can get up on their feet, they start. My wife was not a runner when we got married, though.
My wife and I credit our marriage longevity to the teachings of Jesus Christ which we try to follow every day to the best of our knowledge and ability. We are different people, we both have our weaknesses that could make it very hard for us to get along but we know that Christ is real, He paid for our sins, and we will get to see Him once this life is over. Through His power we can be together forever as an eternal family. Having this vision helps us lay aside our differences, work our way out of arguments, and become united in the same goal.
I know there are a lot of people on this site that have a hard time understanding the above, believing it could be real, etc. All I can tell you is give it a try. It is like consistent training. Non-runners laugh at us for training consistently - until it is time to run, and it does matter how long and how fast you can go. So it is with the eternal matters. There will come a time when this type of preparation will yield major dividends , but a lot of those you can get before you die - and it often comes in the form of a happy marriage.