Girl problem. How do I approach this?

Have you tried getting reactions from her? its usually a nice way of confirming affection, like telling her she looks good or whatever. I think you are in a good spot unless your not her type of "sexual preference".

I guess its different from highschool because i got together with a girl there because we hanged out a lot, but i noticed that she was always searching for me in school, by looking my way or when she started to sit next to me.

I think you guys should bond by doing other things than partying and smoking in an apartment, i remember bringing a girl for a UE adventure and we held hands in the end, i even joked about the wierdness over bringing a girl to such a inappropriate place, kek.