I purchased the game for android. Do i need to buy it again for windows?

The Android and Windows versions are separate, they need to be purchased separately. The price point is set so low so that most people will be able to afford both if they want though.

Windows/Mac/Linux:

http://fpv-freerider.itch.io/fpv-freerider
https://fpv-freerider.itch.io/fpv-freerider-recharged

Android:

https://play.google.com/store/apps/details?id=com.Freeride.Freerider
https://play.google.com/store/apps/details?id=com.Freeride.FreeriderRecharged