There are certainly people who enter into a relationship with each other during high school that stay together for the rest of their lives. Unfortunately for young couples, however, the odds of this happening are quite low. Here's why.
Changes in what you're looking for
What you look for in a partner can change dramatically as you mature. Throughout high school, the majority of people will enter into a relationship with someone because they find them physically attractive at the time.
As we age, our preferences are also likely to change. We often become focussed on deeper aspects of our potential partners. Yes, we still want to be physically attracted to them, but we may also look for character traits that simply aren't present when we're younger.
When you're at high school you generally have very few commitments other than to your school work and friends. Your parents or guardians will put a roof over your head, feed you, look after, and generally, you're not expected to do too much.
As we grow older, we start to follow career paths, and want to explore the world a little more. For many people, this means moving away from their home town, and it's unlikely that high school couples will follow the exact same path.
For instance, each person in the relationship may have to move away to separate universities, and long distance relationships rarely work out.
Finding your perfect partner
I won't enter to a debate about whether or not soul mates exist, but you really are limited to the amount of potential partners you meet when you're in high school.
As we get older, and assume more freedom, we have to opportunity to meet lots of new people. Although high school is a great time to make friends and build relationships, it's highly unlikely that your perfect partner just happens to go to the same school as you.
Of course, there certainly is a chance that a young couple can last the test of time, but there are a fair few hurdles to get over first.