I was out doing a bunch of Thieves' Guild stuff and i decided to drop by my house in Falkreath and as soon as I walked in, Marcurio started attacking me. I just got done doing the special job at pinewatch, would that have anything to do with it?
If you have a bounty in an area some people may try and kill you. Clear all your bounties and go back, hopefully it will have sorted itself out. On pc you can clear them with a console command.
There is some good info about bounties here
It also includes how random citizens / thugs etc can attack you due to bounty