Ok, so i checked out the fallout wikia page and found out there were four companions throughout the game, obviously I decided I'd check them all out. So I now how Ian, Dogmeat and Tycho, but every time I go to leave Junktown the game crashes.
Is it the case that you can only have one companion at a time? Is it possible to have all four at once, or have I simply trashed my save file? Any and all help would be appreciated.

So it's more than likely that the save file is just trashed then? Fair enough, thanks for your help.