@Marko813 - I have an idea that it was NOT absolutely necessary for you to talk with her about school. I think you used it as an excuse to talk to her again. I could be wrong, but I get that impression because you seem over eager to talk to her about anything. You seem obsessed with her every word and gesture as to what it means and getting upset of offended if she seems cold. Nobody can read her mind, but as it’s only been a few days ago she told you to find someone else, I suggest you back off and stop trying so hard for now. You’ve just recently gotten off the streets. You’re living with your parents now and need to obey their house rules. You need to stay in school and not do drugs again. You need to watch your temper and keep it under control. These things will give her a good impression of you.
Or you could ask your parents for advice as they know the situation better than people here.
Or you could ask her out for lunch and I hope she accepts, but be prepared for a refusal.
Well, first of all I didn’t do drugs… second, I really HAD TO speak to her, because last year we shared a special kind of paper that we should buy as a pair (it’s special, because I am in a architecture school, so I can’t just use any kind of paper), and I didn’t know that I need it this year, but I have to.
And I just wanted to quickly thank you for all your advise. I am sure it’s not that easy to answer all that people and all kind of stupid questions like the ones from me. I don’t know what I would have done without you… thanks! 
For now I’ll let her completely alone for a month or so. She’ll wonder why I stopped acting that clingy I think. And in that time I’ll focus on school and on recovering myself. If I succeed (Success= being happy again, with her or without), I’ll let you and all the people in the forum know. But anyways, thanks a lot!
You’re obsessed and it isn’t healthy. You need to work on your own life and find some way to disconnect from your obsession over her. I know you said everything is fine but it hasn’t been long enough to be fine. You seem to be seeking justification for why it is OK to contact with her even when that isn’t healthy for either of you at this time.