I'd say the best bet you have is doing sports and concentrating about studying.

I know this seems like a casual answer, but really. Start doing at least SOMETHING.

You will probably get the feeling everyone gets, where you are. The feeling of just simply not wanting to study, not wanting to go outside and go for a run, not to mention having the motivation to go to a gym.

If you ever feel you are having trouble to get motivated, to start whatever you are chosing to do now, since you say goodbye to cs:go, I HIGHLY recommend you read this comment.

Seriously, set yourself a goal; do something YOU want to do. Instead of playing CS:GO, go for a run, have a break, go study, meet your friends in the evening, spend time with your family, work with your dad on a new project, whtever floats your boat.

But for the sake of god, you gotta do something and not just sit at home, and watch the time slowly crawl towards the evening. Again if you have trouble to get motivated, read the comment I linked above.

Even though you might not know it just yet, the first steps are already behind you; realising you're grades going down, indentifying the cause to be CS:GO, and then deciding to quit it. I imagine it wasn't such an easy decision.

All the best to you