He may have started out as Prince Charming, but eventually you find he's more like the slobbery toad. You know you've made a mistake letting it go as far as you have, but that shouldn't stop you from ending it before it goes any further. The best way to cope with that knowledge is to learn from it. "It's all right to make a mistake and it's all right to change your mind because sometimes that's a sign of maturity," says Hooper. "Because you've actually seen something more important."
And if you're absolutely positive he's not the one, there's no point in giving mixed messages, or he may keep trying. But if you blame it on your feelings, rather than his performance, you can probably get away with a pleasant rejection.