Since you know it's fake then it should be easy to get over it ! Don't watch it again and watch something funny to help forget about it. Comedy always overcomes sadness ! You Tube has tons of funny videos of all kinds !
How do I get over a really sad video? I mean I know that it is fake, but I still can't get over it!
The simple answer is to watch something else and realize that it was simply a video that tugged at your heart.
Why did it make you sad? Think about it, then move on. If you can't get over it, listen to some loud, pop music. Watch a movie you know will make you happy. You'll be over it in a second.