This article may be right about the psyche of OP that fatal night:
"Oscar did feel vulnerable, despite his long list of awe-inspiring athletic accomplishments, not just because of his physical congenital disability, but, because of psychological childhood traumas.
Oscar was traumatized at age six by his parents divorce, his subsequent estrangement from his father, and at age 15, his mothers death. Shed been a cheerleader for him, encouraging him not to let his disability define him. Her passing would have been experienced as a profound abandonment to a teen boy who was so dependent upon her love.
In Oscars adult life, reports of a darker side surfaced, including a hair-trigger temper, drinking, and a reckless boating accident. There are even reports of the police coming out on domestic altercations between Oscar and Reeva before the shooting. So, there was already trouble in paradise, precisely because Oscar did feel vulnerable. Hed fallen in love with the angelic Reeva a law school graduate, beautiful model and soon to be TV reality star.
Unconsciously, he was terrified she would abandon him, just like the first love of his life - his mother had done."
http://thecelebritycafe.com/feature/2014/02/hollywood-couch-what-made-oscar-pistorius-run-afoul-law