Ruby the issue isn’t that you are nice. You are but that’s not an issue. I think he might be behaving in cold and distant manner to put boundaries between you two and discourage you from being too personal. If you acted like you have a crush on him and was getting too personal, he can get in trouble if he encourages you. He is maybe sending you a message that you need to keep your distance.

You equate nice with inappropriate. You can be nice but keep your distance. These people aren’t your friends or loved ones, they are your bosses.