What makes a girl a stalker when she looks at you or watches out where you are?

i was like that to a guy too, looking at him all the time to find out where he was...i didnt know at the time, i thought its just normal to look for him or anyone else, but then i realized even when my friends are talking to me im not actually listening to them im pretending to be happy and laughing and leaning my body somehow so that i can find him and show off somehow. i didnt pay attention again but now i know that bcuz i liked him so much i did those and well for him, it was obvious to notice that i like him! but honestly i wasnt the first who started, he stared at me too, and thats how the whole liking him started, but then he dated someone else so he didnt give a shi* abt it...i guess for some ppl it doesnt matter if u look at them or look for them, they think u like him, but to look for girls well yeah thats annoying...u hv to at least pretend to be ok with lonliness and thats when u would act normal and find friends :)