Answer:
It's truly inevitable or impossible to avoid the fact that the person is going to get hurt. You just need to minimize the damage is all. Whatever you do, don't bend around the bush. It gives the person a false sense of hope. I think you should give the person a straightforward answer. Also mention why you're breaking up. Make sure to tell them that they are still a nice person but I just don't feel that this is going to work out.
Tip: Keep in mind that certain people react differently