Crying over a man who was not good for me – WHY?!

My problem is: my boyfriend left me (for another woman) after 15 years of a dysfunctional relationship.
What I don’t understand is that despite the fact that during these years he regularly disrespected me, insulted me, scorned me, psychologically abused me (ascendency), made me feel like a bad girlfriend, cheated on me (at the end), lied to me (at the end too, but maybe even before)… I don’t understand why in spite of all this, I’m so sad. Why do I miss him? Why do I only think of the good times, of his qualities, of the moments of our crazy love?
Why, God, why does my brain do that? How does it respond to a protection? Why doesn’t my brain say to itself: “Good riddance! The immature, self-centered, deceitful, lying, disrespectful, immature boy I spent too many years with is going to go and destroy another woman. I have nothing to regret!”
I cry. I feel abandoned and alone. He happily goes on with his life and I don’t understand myself.
What does it say about me to cry over a man who has hurt me so much? That I am a weak, whining victim who doesn’t respect myself?
Thank you for your help.