Unless you go to a hotel which specifies that it’s gay-friendly, you might experience wrong assumptions. Even if you book your stay online and specify that you request a double bed, at the time of your arrival the staff might think it was a mistake. Such things are usually easy to solve but we do not appreciate having to bother.. Nevertheless, such is life and no matter where you go, it might happen.
If you want to avoid having the conversation, try behaving like a cuddly couple on your arrival (holding hands, arm on the shoulder or referring to each other as boyfriend/girlfriend or husband/wife) - hopefully they will get the message without having to explain. If you go to a country where English is not widely spoken, try to prepare the vocabulary before you arrive as it might be handy.