A hip and mature adult life and gaming are not mutually exclusive. WHY do you feel the need to hide your gaming habits like you're some sort of crack-fiend? Has your girlfriend or your roomate or anyone around you given you any reason to feel that you'll be abused and belittled if you dare play a game in front of them? Reading the article, I feel a sense of... painful desperation, of a little voice murmuring "don't hurt me, don't hurt me" all the while through.
Your interests are your interests, and they are just as valid as anyone else's. There is no shame in a few hours of solo gameplay on your own time. Your life sounds fine, all things considered. Productive, full of good things, and fun activities, and nice people... and it would be entirely unimpacted if you looked up from your Halo 3, went "Good morning, honey" when your girlfriend walked in, and tooled around for a few more minutes before getting up to get brunch. It is important to be honest with your yourself, and to accept yourself, and all the little parts that you contain.
As others have said, too, I can see a little of myself in here. I'll confess to letting my nerd flag fly its highest when no one is around, even if I don't pack it all up when others come along. I'll chitchat with my co-workers when they mention that they're getting Guitar Hero for their son, or a Wii for their daughter. What's the harm in saying "Oh! A Wii! I think I'm jealous. She'll like that." or "They've got that one on sale at X store, go buy it there"? The admission of one's hobby is not the same thing as a frothing at the mouth, carried away by the spirit of the obsession nerd-gasm.
Let go of your fear. Unburden your heart.