Lila did guide Dexter into really letting go physically - it helped him with Rita - and she endorsed and in the end goaded him in his avenging angel slayings. She supported, protected, and killed for Dexter. But in the end, the darkness in Lila's being was something Dexter could not countenance, especially when it threatened those he loved.
Rita, may she rest in peace, was never right for Dexter. Although she saw the good that was in him, she was essentially in love with a man who never was. I don't see how their marriage could have lasted, even with no Trinity in the picture.
Lumen is really the most like Dexter. Her thirst for vengeance is not the depraved lust for violence that animated Lila, but rather the same quest to make herself whole, to recover from the damage that was done to her psyche, the trauma to her innocence, by the scum of the universe, or, at least, of Miami. That is, to recover from something of a magnitude equivalent to what was done to Dexter.
Dexter thought that Rita might heal him, and though her murder left that undertaking inconclusive, it's certainly undeniable that at the time of her death she had not. Dexter found someone like him in his brother, but he turned out to be too evil and threatening to those that Dexter loved to do any good for Dexter. Much like Lila.
Deb loves Dex, but much as I hate to say it - because Deb and her mouth are one fine character - Deb's just another version of Rita, in that Deb does not know or see the real Dexter, either.
So that leaves Lumen. She's moved faster, has come closer to Dexter more quickly, than any except perhaps Miguel - but he obviously was no innocent, either. Do Lumen and Dexter have a future?
I hope so. I like her far better than Rita or Lila. But Peter Weller's Liddy is mean and tough, and Quinn may be unable to stop him, even if he wants to ...
See also Dexter Season Five Sneak Preview Review ... Dexter 5.4: Dexter's Conscience
And see also Dexter Season 4: Sneak Preview Review ... The Family Man on Dexter 4.5 ... Dexter on the Couch in 4.6 ... Dexter 4.7: 'He Can't Kill Bambi' ... Dexter 4.8: Great Mistakes ... 4.9: Trinity's Surprising Daughter ... 4.10: More than Trinity ... 4.11: The "Soulless, Anti-Family Schmuck" ... 4.12: Revenges and Recapitulations
See also reviews of Season 3: Season's Happy Endings? ... Double Surprise ... Psychotic Law vs. Sociopath Science ... The Bright, Elusive Butterfly of Dexter ... The True Nature of Miguel ... Si Se Puede on Dexter ... and Dexter 3: Sneak Preview Review
Reviews of Season 2: Dexter's Back: A Preview and Dexter Meets Heroes and 6. Dexter and De-Lila-h and 7. Best Line About Dexter - from Lila and 8. How Will Dexter Get Out of This? and The Plot Gets Tighter and Sharper and Dex, Doakes, and Harry and Deb's Belief Saves Dex and All's ... Well
See also about Season 1: First Place to Dexter
The Plot to Save Socrates
"a Da Vinci-esque thriller" - New York Daily News
"Sierra Waters is sexy as hell" - curled up with a good book