When couples first start dating, they may overlook their differences, but once a relationship becomes long-term and the couple falls out of the honeymooner stage, these differences can become disastrous. The root cause of a breakup of a relationship is the selfishness that erupts in the heart of one or both partners; the love factor which was in the relationship diminishes over a period of time. Here are the most common reasons as to why marriages/ relationships break up: