Regards checking the balcony or shouting for help - this is significant. Nel is examining OP who is the only surviving witness of the events. He is examining OP's intentions when he went out into the balcony. On this night, in OP's version or in the State's version we can assume that a reasonable person would have shouted for help and OP indeed said that this is what he did. However, the need to check the balcony only arrives in a specific situation, whereby:
a) OP was looking for someone
AND
b) he thought it reasonable that that person could be on the balcony.
The second is only really possible if OP thought he had shot an intruder and was looking for RS.
This is relevant to when and how OP realises he shot RS.
It was raised by Nerf that so early on in a relationship why would an argument have escalated so quickly. I put it to you that she was threatening him with media exposure of abusive behaviour. Hence she had her phone with her. Apparently she was associated with anti-DV causes. It is possible that they were arguing, she retreated, locked herself away, refused to engage with him and meanwhile threatened to call someone if he didn't. She paused, he was frightened of the effect it would have on his career and shot. He shot again, and again and again. Then he came to his senses, realised what he had done.
Is that possible?
Is that more likely than his version?
Also, maybe Reeva turned off the alarm?
By the way, I don't think we'll get to the "straightforward truth" until we get to the stage where there were eye-witnesses present.