I'm not really sure what's going on in the comments - or if I am from some other planet but I don't think all the vitriol towards OP is really warranted.

Firstly, it sounds like she is overly codependent on you and since you enable it 90% of the time (sorry), she acts out when she doesn't get her way. Outside of communicating more about your need to have your own time occasionally - maybe encourage her to pursue hobbies she enjoys, or push for asking coworkers out for drinks that she gets along with. Also it could help to start going on a date night at least once a week that is special and out of the norm from hanging around the apartment together because it seems as though that is not enough for her (which is fair). Also I want to note if she is not heavily into gaming, her tagging along with you to a tourny doesn't really count.

Some people in the thread comment about how why do her making plans needs to involve you at all - and I think they are missing the point. Her hiding the post on facebook from you is what gives it the edge - it doesn't come off as her trying to make an effort to have fun or make plans on her own. If this were any other situation and someone was hiding posts from their SO on social media people would be up in arms. Additionally, it is a very immature, overblown response to you taking the afternoon to play/watch video games with a friend.

But I will note that from your overall tone you sound tired and fed up with being the sole person she relies on - because this is not healthy. Once you are both less emotional about the situation you really need to just have a long talk about what needs you aren't fulfilling for one another - be specific about these as well!