so i deleted the witcher 3 some time ago because i needed some space on my compuer, and now its gone on gog galaxy. plz halp

Go to Library Tab -> All my games ; look for search and type Witcher -> Voila.

Find Witcher 3 and download it.

inb4 G2A

If you did not purchase Witcher 3 from gog (or get it for free from an Nvidia purchase) and you instead bought it from a CD Key reseller, then hey you're screwed. CD key resellers often sell CD keys that were purchased with stolen credit cards. After the transaction is reversed, the CD key becomes invalid.

I am starting to lose empathy for people that still use that place. I'm not saying he did, but if he did, there is really is no excuse any more.

EDIT
of course, Themken is probably right and I should shut up. :P

Calm down! It sounds like the OP had just uninstalled it being temporarily not in the mood to play Wither 3.