I will start by saying I met my husband through an online game.
That said, stay friends with both of them. Believe me, I understand just how well you can come to know people through the internet, and I believe that most people are actually quite honest (and if you talk to people for a while, you start to learn just how honest people are--this is no different than meeting strangers in real life.) Stay friends and, if you want, which you seem to, meet them as friends and only friends while bringing your own friends along. More than likely as time passes you will lean more towards one of them, and/or one of them will veer in different directions.
Since it seems you've already entered a "more than friends" relationship with one of them, I'm honestly not sure what would you should do. Were it I, I would probably let the boyfriend/girlfriend title stay (so as to not make him feel shut out) but act no different than if you were just friends. Since he may press for more, just don't go along with it and definitely don't do anything you might regret.
Hmm.. I know that really didn't cover much, but I don't want to start presuming things.
As an amusing side note, my dad actually called my then-friend/now-husband's commanding officer and asked about him. (yes, I was 17.) Kind of embarrassing, but I'm glad he did. It also helped my father be able to trust him more. I will also say that I've grown immensely from the already mature 17 year old I was (I am now 21.)
