so I bought witcher 3 in december.. and it uninstalled twice now..it seems like it uninstalls when i havent played in a while.. does anyone know about this problem and how to solve it?

A game or a program does not uninstall by itself. You need to provide much more information.

well it is strange..when i play witcher 3 then quit for a week or so it says, that when i go on gog i need to install the game first, even though i already did
it is important to note that it wasn't always like that because alot of times i just could play it without any problems

Do you have windows 10? Cause that was a known problem that popped up after a grand update. it randomly uninstalled programs due to "incompability" as defined by the operating system.... It should have been fixed already, so maybe you need to simply update your windos 10?

Otherwise steam had some similar problems: http://forums.steampowered.com/forums/showthread.php?t=2147730
maybe you can mcgyver something out of that

This has just happened to me for the 3rd time on GOG, I'm installing it on Steam and that's the last time I use GOG for anything. Pity, because at launch they were awesome.