Related Video: Should You Marry Young?

One winter night in the Colgate University dining hall, sophomore Katie Thompson fell in love—fast and hard—between the salad bar and the soft-serve ice cream machine. One cute guy stood out in the crowd.  She caught his eye, he asked her for a date and the rest, as they say, is history. They dated through college and their twenties as they launched their careers. They got married at 26, had two kids and lived happily ever after—almost. By the time she turned 36, Katie hardly remembered the girl she was when they'd met, and she realized she had not only grown up; she'd grown out of the relationship.

The thing about young love is, well, it's young. When you are 19 and rather naïve, you just don't know the exact woman you will become. Your identity will still be shaped by complex choices around kids and careers.

Personalities and temperaments may not change too much over a person's lifespan, but levels of passion in the college dorm room and opinions of his once-adorable little character traits very well might. Like that great-looking, comfortable hole-in-the-knee pair of Levi's jeans you threw on for early morning classes, you wake up at 26 to find your significant other is no longer such a perfect fit. You can't wear those jeans so much anymore (they don't look as good and you would look crazy at preschool pick up), and a comfortable relationship might not be enough.

Certainly every marriage gets to the point where taking out the garbage and running the kids to the bus stop takes precedence over lounging around and doing fun "couple" things. But perhaps this change is even more pronounced to couples who were together in their carefree college years when compatibility was not yet a key priority.

According to "Dr. Romance" Tina B. Tessina, psychotherapist and author of Money, Sex and Kids: Stop Fighting about the Three Things That Can Ruin Your Marriage (Adams Media, 2008), our culture has also blown romance out of proportion. "Romance is a momentary, fleeting thing, and it does add excitement to a relationship, but it's not a way of life," she says. "You can't keep it going every moment through the stress and business of everyday life."

That lovesick college coed can turn into a different woman ten or twenty years down the line, explains Dr. LeslieBeth Wish, a psychologist and social worker in Sarosota, Florida who's doing research on women's relationships. "Many college students' brains haven't finished maturing yet," she explains. "Unfortunately, many couples part because they feel as though they've grown apart. And they probably have. After all, they've likely hit their stride and focused their values, skills, interests and goals more clearly."