Hehe sorry it got you frustrated!
The game is purposely meant to have every choice make an impact, so if you want to discover absolutely everything it needs far far more than 6 playthroughs. However, the good thing is that each girl, by herself, isn't that hard to win over. Some are tougher of course and there are always several versions of what can happen but 2/3 playthroughs per girl should get you everything.