Why guys keep on flirting?

I don't know why but they keep on flirting me. Why can't they be normal. My friends say i am some what good looking . But that doesn't mean they keep on flirting. I want them to be my friend. they text me just hello. How are you, when can we have talk, I have to go but we will talk at night on facebook, (though i come online but not for them). and many more. n also it happens when we have started knowing. Just become friends. If they begin in this way than how will the good friendship grow. N i do talk with them but very generally. i don't prefer to talk in a very cheap and insensitive manner. May be they take my politeness in a wrong way. I don't know. Please tell me how a girl should behave so that they wish to be friend but not flirt.