Nonetheless is used when talking about an amount of something. * He really botched it tonight. I love him nonetheless. Here we are saying that the amount I love him has not been diminished from the level I loved him prior to his having botched it. Nevertheless should be used when talking about doing something despite the facts. * It could be dangerous. Nevertheless, I've got to try. Here we are saying that I will try despite the fact that it could be dangerous. ***As a whole ,There's no difference between them, though 'nonetheless' is less common. As they are normally suprasentencial (contrasting sentences), they can be replaced by 'however',