No thinking in a situation like that. Just reacting.
Yep, first thing they teach in Lifesaving is that there is no gain in having two drowning victims - your're no good to anyone dead. Having to live with the decision is another question.
I don't think so. He didn't say that something clinging to him and he had to fight to get free. He said a pregnant woman clinging tighter and tighter to him, right? I don't see that as panic. He knew what had a hold on him and had to make a decision. It doesn't say. He may have tried to get free enough to bring them both up and couldn't and finally pushed away. In reality she had just as much of a chance to come up for air as he did. Panicing probably what killed her and staying calm probably what resulted in him surviving . Hard thing to live with though..