Relationship have Time LImits?

Many couples I know doesn't last more than 5 or 7 years. There are only two choices its either to break up or get married.
Some say they fall out of love. Some gets comfortable to be with each other and just want to be friends, because there were no mystery left.
Most of them say its not the years, but how you handle your relationship.
Well I guess before committing to a relationship, ask not what the other person can give, but rather how much you can give.
The secret formula of a happy, lifelong, loving relationship is always focus on what you can share instead of what you can take.