I would imagine the energy it takes to maintain such a emotion to be almost impossible to maintain, except with great focus and concentration. Hate is a form of self-suffering in a visceral sense, as it is hard on the body. That in it self, like stress, is a good reason to get a handle on it. Hume, who I respect, says hate is an irreducible feeling, I am not sure, as I think the word itself is misleading.
Hate, like love, involves making assumptions about the other, a “theory of mind”. With love, we take for granted the object of our desire acts with compassion, sexual hunger and reciprocation wants, so we love. In hate, you believe the object of your desire acts despicably, with malice and intent to do damage to you, so you may hate.
The study by John Romaya of the Wellcome Laboratory of Neurobiology at UCL: In this work, we address an important but unexplored topic, namely the neural correlates of hate. In a block-design fMRI study, we scanned 17 normal human subjects while they viewed the face of a person they hated and also faces of acquaintances for whom they had neutral feelings. A hate score was obtained for the object of hate for each subject and this was used as a covariate in a between-subject random effects analysis. Viewing a hated face resulted in increased activity in the medial frontal gyrus, right putamen, bilaterally in premotor cortex, in the frontal pole and bilaterally in the medial insula. We also found three areas where activation correlated linearly with the declared level of hatred, the right insula, right premotor cortex and the right fronto-medial gyrus. One area of deactivation was found in the right superior frontal gyrus. The study thus shows that there is a unique pattern of activity in the brain in the context of hate. Though distinct from the pattern of activity that correlates with romantic love, this pattern nevertheless shares two areas with the latter, namely the putamen and the insula...<snip>..... “Significantly, the putamen and insula are also both activated by romantic love. This is not surprising. The putamen could also be involved in the preparation of aggressive acts in a romantic context, as in situations when a rival presents a danger. Previous studies have suggested that the insula may be involved in responses to distressing stimuli, and the viewing of both a loved and a hated face may constitute such a distressing signal."
So no surprise that neurologically speaking love and hate are related. But I suspect you are interested in the philosophy and practical application of it more then the neural correlates of hate? Still they can be a part of the solution to the puzzle.
I think all the usual rote answers of forgive and let it go, or time heals etc, are pretty useless but at the same time I have little to offer except study the root cause of your hate with a empirical mind set and you will work thorough it. For me understanding the "meat" side is just as important as the "mind" side.

Here is why understanding works : say hate is fear based, understand your fear, hate fades, no fear left. I would ask myself is my hate rational or irrational as a starting place. Hate is a tough one, as I have not experienced it first hand, I can not offer a practical solution, just a few idea's to set you on a possible path. Good luck with letting it go, however you find the solution.