There is a great deal of truth and insight into what you've posted IMO.
My take on OP's disability & inadequacies . . .
OP was given the incouragement & drive from his Mom to try anything & everything and to not fear limitations due to his physical handicap. However, even with this great support and upbringing from his Mom, he of course incountered "outsiders" who could be cruel and his awareness (as he grew older) of his physical "differences" were a painful daily reality, regardless of how well he could overcome them while using prothesis. As a result, I believe OP has lots of unresolved anger, jealously, resentment and a huge "chip on his shoulder" for the situation he was born with.
I believe he has severe inadequacy issues. And even if he doesn't acknowledge them "outloud" to even himself ... he spends his daily life trying to over compensate for it. Like the flashy expensive cars, reckless behavior & always driving at such unsafe speeds, the flaunting of all the "chicks" he's been with to Reeva (and likely to all prev girlfriends), all the blonde sexy girlfriends (who look almost like clones) on his arm and the need for them to shower their attention on OP every minute. I am sure the guns help with feeling safe in S.A. but I also believe they're a power thing with OP - makes him feel like a "big man", always in control.
His moodiness and quick temper IMO are related to situations when OP is unable to control the outcome that he desires or feels he's entitled too. After achieving such "stardom in S.A." he feels a great sense of entitlement, as well as power - as all of Africa stands behind him in support and has him placed high up on a pedestal, where he can do no wrong. I think when the situation with Reeva escalated to a state where Reeva would be forced to speak out (likely to police, which means the media gets light of it as well) he felt his "image" (and all that goes with it - $$$, fame & future opportunity) was more important than sparing Reeva - he probably rationalized it as her fault somehow for letting things escalate or pi$$ing him off so badly. Anyway - due to his sense of entitlement and inflated ego - OP felt certain he could cover up yet one more "indiscretion" and he would have all of Africa's full support, even sympathy from the public, as he had just lost the "love of his life" so tragically.