how do you tell someone to go away?

how do you tell someone to go away? hmm interesting thought huh. i mean is it fair to tell a person you want them to go away when you don't have a good reason for not wanting them around and a lot of reasons for them to stay? i'm in a bit of a predicament aren't i? i want him to go away but i don't what to do. i highly doubt its just a phase considering that i've felt this way for a while and it's not fair and now there are all kinds of reasons he might assume i want him gone and i know he won't understand it sux. to have been feeling this way fro so long and yet i can not bring myself to say go away, get out i'm done i'm tired and this has run its course. life is such a pain sometimes and i hate being so emotional i wish there was an easy way. i don't how to go about it can't someone help me?