He won't leave me alone

There is this guy that constantly texts me and I'm not interested AT ALL. I'm trying to be nice to him to let him know I don't like him like that and he obviously doesn't get the hint. If I don't text back within 5 minutes, he sends text after text. Sometimes he'll say things that make me feel awkward and I don't know how to tell him to leave me alone without sounding like a bitch.