Don't limit yourself to just one hard drive. Buy a cheap 128GB ssd to just stick windows on, and another drive to install your games on. You can split that third drive to be used for windows games, and the other half for Linux games. Then set up boot order to access the Linux drive first, and when you do want to boot up windows you can hit the hotkey at startup to select a different drive to boot first that one time. That way you know windows should never jack with your Linux system at all, and you don't have to worry about anything getting messed up if you have to format one drive or the other.