Its really easy to know when something is over.

If it feels over it is over.

Apart from that: correct me if I am wrong, but if something is not perfect, there is no point in carrying on anyway. Right? There is a most simple explanation to this, as long as 2 people want something badly, they seek a compromise. They want to see the other one happy, so as long as they want "each other" happy, it will all work out fine. Trouble really begins when someone wants him or herself happy, because in no time, you will find two people wanting one person to be happy in a relationship. From than on its not a good relationship. Maybe a good ship but sure as hell, not a good relation.