I tell my long distance girlfriend that I'm going to sleep but instead stay up and play video games with my buddies.
Why don't you tell her the truth?
I like to play video games with my buddies and don't want her to know about this.
Unless your video game hobby is affecting your health, work, or relationships, she should accept it. It's better not to hide it. She'll find out sooner or later, anyway.
Playing games with my friends makes me happy and I don't want anyone to take that from me.
If she can't accept your hobbies and be happy for you when you're happy, then maybe you shouldn't be with her. Tell her the truth and see how she reacts.