So i have my SSD for boot, while I have my HDD to keep all my files (documents, pictures, games etc..)
If I ever get a virus, would it infect just my SSD( OS) or would it also infect my HDD as well?
It depends upon the virus and how it spreads. I would assume yes - as most viruses look to propagate themselves. You should always have a current virus scanner and malware scanner on the PC - there are many free ones on www.filehippo.com (I use this site all the time).