I want to buy GTA 5 from PSN instead of buying the disk, but i want to know if i will still be able to play GTA online. I ask because i heard that GTA online was a stand alone tittle, and was wondering if i needed to buy it separately.
Yes, you can play GTA online with the digital version of GTA V.
GTA Online is "standalone" in the sense that it has no connection to GTA V outside of the base content (map, NPCs, vehicles) being used. Save data, stock market info, and other info is not shared between the two game modes. DLC content can be released for GTA Online that doesn't affect the single player portion of the game. It is otherwise included with GTA V, and in fact can only be accessed through GTA V.