Itachi wasn't cold-hearted.
And yes, he did have a heart.
But now it was broken.
He knew his baby brother was going to hate him, it was his plan, afterall.
But he just wanted Sasuke to be happy, he didn't expect, nor want, Sasuke to become obsessed with revenge.
So obsessed that he would leave the one he loved.
Itachi wasn't stupid, he was extremely perceptive.
He knew from the way his little brother watched the young girl that he was in love with her.
But his obsession with power, with revenge.
It drove him to insanity.
So his last parting words were 'go to her.'
It was where he always belonged, with her.
But Sasuke was too far gone, he couldn't go back.
He wouldn't be accepted.
Sasuke was his little brother turned murderer.
All because of an oncoming war.
He was insane, driven by hatred and saddness.
But mostly, he was just heartsick.