I think you haven't read what you are supposed to do. You don't have to convince them to do something once, you have to make it a permanent behavior. When you read carefully what you are supposed to do with each girl, then it becomes clearer.
And yes, i failed on my first playthrough exactly like you.
When you play a game and your target is to collect 1.000 gold, you cannot say: "Man, i collected 300 Gold and i didn't win, this game is stupid." The difference is, that in this game it's harder to understand what exactly you have to do, that's why i say "read carefully what you have to do, it's a short description but gives a lot of clues".