Sometimes the only thing that can make a relationship successful is ending it at the necessary time, before it becomes too damaging.
One of the mental tyrannies we face in a non-honest relationship is the situation where any mildly emotional or sexual thought not involving your partner amounts to high treason.
The problem with allowing your identity to be consumed by a romantic relationship is that as you change to be closer to the person you love, you cease to be the person they fell in love with in the first place.