I had similar problems to this whilst I was at school, although I dont think I was physically dependent, I think it was a mental thing. And it didnt involve nurofen, just ordinary paracetemol. It sounds weird I know but I just couldnt stop taking them (not in an overdose way or anything), I just felt like I had to take them even if I was feeling fine. At one point I was taking the maxium dosage every day, just because I didnt like not taking them, if that makes sense. I didnt even realise I had a problem until someone else pointed it out, and after that I managed to wean myself off them and cut down, to the point that I stopped taking them altogether. This was about 8 years ago now, when I was about 15/16. At the time I was being bullied really badly at school and that definately contributed towards it.
Even now I cant stand the sight of paracetemol and it makes me really ill if I ever take it- ie physically sick, upset stomach etc. So I just use other painkillers instead if I ever need any.