Extremely Nosy Neighbors and Cousin?

You send one last message. You say, very clearly, that you do not wish to pursue a relationship of any kind with him, and you're sure that he will respect your wishes. If he doesn't behave, inform him that your next step will be a restraining order. Making excuses instead of stating what you want has led you to this position, with him and with the neighbors. Be a little more honest with people and they won't be able to inconvenience you with their stuff.