YouTube is a great place to post videos. Since it is owned by Google, YouTube videos are great for SEO. You can post as many videos as you want to for free, even “unlisted” and “private” videos. and until recently, you could uncheck the box on embedding videos that would show related videos at the end of when your video was done playing. Alternatively, you could add ?rel=0 to the end of the embed string. But now Google/YouTube has decided that showing related videos at the end of your current video is important to their user interface, and simply ignores this parameter.
More accurately, when you use the ?rel=o parameter on your video, YouTube now shows only YOUR videos, not videos created by others. But, it will show other videos regardless, just yours instead of competitors. The option to disable or remove these related videos has completely gone. Google believes that related videos are an essential part of their UI (user interface) and are now promoting the feature. There is no work-around except to use a different video hosting site.