In the end of season 5 of Dexter, Lumen suddenly leaves, even though they made the perfect couple.
The reason she gives, that she no longer has the need to kill while Dexter still does, feels very weak and far from being sufficient, so I'm pretty sure there is other reason or reasons.
What are those real reasons? Is this explained somewhere at some point, in show or outside the show, e.g. interview with actor or producer of the show? (I did not watch further seasons yet.)