Is my jealousy justified?

Hey!
First of all let me tell you a few things about us: Both my girlfriend and I are around 20 and we've been together for 3 months now. We share many common interests, one of them being gaming. A few weeks ago I introduced a new game to her in which she took great interest. I've been playing it for a few years with my best friend but I kinda got bored of it. She on the other hand is almost obsessed with it and spends a lot of time playing it. Because I’m not really into that game anymore she plays with my best friend instead. Now first I was happy that they got along so well but I noticed soon how much time they’re spending together in-game. Of course I can’t compare their gaming sessions to a real-life meeting but they’re still talking and playing for hours and hours (even up to 3-5h) often until soon past midnight. It got to a point where they spend almost as much time in-game as we do in RL since we don’t live together. We talked about it and she assured me that she’s only interested in the game but it still hurts me. It annoys me that she talks to another guy for that many hours on an almost daily bases. We discussed possible solutions; I don’t like it how much time they’re spending together (even though it’s just virtually) but I don’t want to restrict her in any way. We’re curious to see what other people think about our situation, am I just overreacting?