Starting a relationship with a significant other can bring much happiness. As with marriage, there's a honeymoon phase where you float above problems and always get along. But the honeymoon doesn't last forever. And if some ground rules aren't put in place early on, the relationship will crumble quickly. As the relationship progresses and depending on what level it gets to, more definition may be added. Here are some must-have rules. Four Must-Have Relationship Rules of Engagement