I've ruined my life
That's a very intense thing to say, why do you say you've ruined your life?
When you play a lot of computer games, there is a tendency that your grades will start to drop.
At least you know and accept that your gaming addiction is affecting your grades. You're still young so you have a chance to recover from that.
The computer game is really fun, I should probably play more of it.
I also play computer games, and you should have a time limit and know when to stop, as any addiction or anything you do excessively is very bad for you. I do hope you set an alarm and follow your limits so that you don't regret it in the future.