Daniel Riddick (SPOILERS)
Or "Reddick" or whatever his name is, showed his true colours when he left Blake to die. It's realistic, human nature is selfish, in a life or death situation would you risk your life to save someone else? Especially when you're not even that emotionally close to someone?!
Another thing about that scenario that could have been possible was that Daniel Reddick got amnesia, he was hit unconscious and then when he woke up he couldn't remember anything or anyone, it could be possible that that was the case, but i highly doubt it due to the dialogue making it clear that he left her out of his own cowardice.
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