Usually guy's who like someone who they think they cannot `reach` the standards, are too shy to actually get near to the girl or always fight with them. Always remember that no one would stare at you if he does not like you. :)
Could be nothing. I'm a guy and a lot of us look at other women. Sometimes it's just because we notice an attractive female. Sometimes the guy could have some dishonest intentions. Not everyone is the same so also take his personality an how he treats hi lady into consideration. I've heard lots of men and women say "I can look at the menu, 'I' just can't order".
Theres a guy that I like and now he has a girlfriend ugh but he stares at me when im not looking and when I notice we stare then he turns away shyly and if I try to get a lil close to him he stares and trys to kinda not let me find out hes lookimg at me.