What does it mean when a guy stares at you?

ok well theres this guy...and lets say his name is 'bob.' ok so me and bob were kind of friends last year and the beginning of this year but now were kind of like enemies well not exactly enemies but were just not friends really. anyways,i cried because of him yesterday so i guess you can say i like him but the only reason i like him is because A. he is cute. and B. his personality is really awesome. some people also tell me that me and 'bob' make a good couple. also my sister and his brother know each other and well they kissed. and this one time me and 'bob' had detention together and it was really quiet but the next day me and my sister were talking and somehow it got to the subject of detention with 'bob' and well apparently bob told his brother that i was there and the whole senior cl in high school found out that me and bob had detention together. i dont know why he told his brother. and all this week we had this big test so we had to stay in homeroom and hes in my homeroom. and everytime i glanced up at him i saw him staring at me and no im not imagining this because i asked my friend sitting next to me was he staring at me and she said yeah. but sometimes she lies so i asked this guy that is one of bobs friends if he was staring at me and he said yeah bob has been staring at you all week.sorry this thing is so long i just wanted all the info to go in so yea..what DOES it mean when a guy constantly stares at you??