Hmmm... It started as it should, getting harder and harder... But around level 19-20, they got easier again, to the point of being very easy in the last few levels. It might be because one gets better at adopting to the mechanics of the game, without the increase in difficulty following properly.
I see it as a guy who keeps giving and giving, but the girl barely notices him. As he gives more and more of himself to her, her world becomes richer. She finally realizes who it is that has made her happy, but it is too late; he has given up, and moved on.