I'm not sure it is the worse thing ever. Just because if that YouTuber has ads or not they are still displaying your game. So you are still getting publicity and traffic towards your game. If that person wants to monetize it to make a little money themself then I don't see the issue. Like you stated you took ages making this game and for someone to just take it and make some money from a 10 minuet clip I understand does feel kinda sleezy. But honestly look on the bright side. Someone is interested enough in your game to want to share it online with other people. Try look for the positive side. (If this felt like I was being rude or anything I promise I wasn't. )