The lewd tracker (which you can view in your phone, in the Love Jensei app) shows you various levels and what scenes you have and haven't done with each girl. The lewdness system (which is being improved over time) is a rework of sorts of the way you advance lewdness in the game.
With both systems, the aim was to clear up, improve and make the lewd scenes in the game a tad bit more straight forward and interactive.