If you started to lose against boss at chapter 5,it may be too late because you are in the final part of the game and if i remember there isn't much to see at this point if you have not lost your virginity,but i can be wrong.
But i strongly recommand that you replay the game once you have finished the game on knight route.
Like the person said above, in one one games you have multiple story paths (called "route") ,for exemple,if you restart the game and lose 3 missions,you will be leaded at the end of chapter into the resistance route/path ,wich have a totally different story,plus you will have more H Content than knight route.
You even have a third route if you meet certain conditions in resistance route,,called drifter route,unlocking pregnancy and free demon form transformation.