This is actually deeper than you think. You see, in her past, Momo was just handed the book, as if she was just a cute girl who, if you did her a favor, would put out for you. But our MC, instead of just helping her, gives her the ability to get the book herself by acting as her stepstool. Instead of just being passive, Momo is given a chance to get the book herself, to actually have agency. That's why she loves him.
...or maybe this is just a bunch of random justifications to try and justify continuing to read a series about fucking a little girl with massive tits.