Online Obsession and Jealousy

Hello, my name is David and I'm 17 years of age. Getting straight to the point, I am obsessed with a girl that I've met online through a video game. It started with her showing interests in me, and being an attentive person, I picked up these signs and would get really hooked up with them, but because of this, it had led me down this torturing spiral. This goes on for nearly 9 months now, we both wouldn't butch and confront one another. The reason why I don't want to confront her is because I find it unethical to form an intimate relationship with someone online without knowing them or even met them in real life, and she lives in the opposite world as I do, this is all the reason I need to stop liking her, but I just can't. I also see her talks to this other guy often and every time I see it, it pisses me off and make me upset, my day would be ruined instantly, especially when she talks to this one guy. The reason I feel jealousy is because I'm imaging that she's starting to like him instead of me, it feels like I'm starting to lose her. I am aware of what's happening but don't know the solution to the problem. I've had a few girls from school taken an interest in me but I would feel nothing for them, while the online girl would occupy my mind 24/7. I even tried to stay away from the source but it does not work. It makes me really jealous and fantasies would fill the gap when I see her talking to him, and the way they talk to each other is almost as if they're a couple.
It's so bad to the point where I wish I'd never played this game and met her, because it is ruining me physically and mentally and is affecting my work performance.