Garry's mod Game mount reset?

I’ve noticed when I uninstall a game to make some space and play garry’s mod that has that game to be mounted it will start reinstalling that game to meet the status quo. I was wondering if there is any options to reset the game mounting to only Half-Life 2 outside of garry’s mod so if I reinstall Gmod or have uninstalled a game it won’t start reinstalling that game eating up my HD space. I also notice when it does this auto install I can’t see it installing until I reset steam.

Sorry for bumping but I really want some help on this