The secret for long relationships is not having a perfect and harmonious love affair. It is not how less often you fight, not because of the number of similarities and the stuff you both like doing together nor the number of mistakes you did. Those things count but it is the faith that keeps you going. A relationship will only last if both of you are unwilling to give up, if both of you are willing to stand up and still try every time one/both of you fall. You should not lose hope when you are stuck with problems along the way.  

credited here.