Leia, do you remember your mother? Your real mother?
Twelve has already stated that he doesn’t care - “she cares so I don’t have to” - and that may be true when it comes to the majority of the population. But Clara’s different. He helps and protects her from injury, not because he thinks she is incompetent, (he actually thinks the opposite, shown by the way he left Clara to receive information in Deep Breath) but because he cares for her. He knows she can handle anything on her own, but he’ll still be where he always is… as long as he’s the Doctor, he will have Clara Oswald’s back.