BBM
Yes - the instinct to survive is extremely powerful - as is the instinct to ensure that your loved ones are safe.
A few years ago, my youngest daughter (a teen at the time) and I were home when someone tried to break into our house early in the morning. I grabbed the phone and dialed 911 while at the same time waking my daughter. I wanted to ensure that if the intruder succeeded in breaking in (he was trying to break down the front door), my daughter would be awake and alert so that she could flee or fight. I didn't even have to think about it - my instinct was to make sure my daughter was safe.
Per Samantha Taylor's testimony (OP's former girlfriend), OP's historical pattern had been to awaken her and consult with her when he heard noises in the night that he thought might be an intruder. She testified to 2 separate instances when he had done so.
On the morning that OP shot and killed Reeva, he didn't even check to see where she was (according to his version), nor did he consult with her regarding the noise he allegedly heard (as he'd done with ST in the past), let alone ensure that Reeva was awake, safe, and ready to flee or fight.
At a glance, OP's version sounds plausible. But when placed in context of his historical pattern (see above reference), and when scrutinized beneath the light of the State's evidence, I personally find his version to be less credible than the State's case.