Uh, you could run a program (like Teamviewer) that will allow him access onto your computer, but keep in mind that gives him access to EVERYTHING on your computer. Automatic cloud syncing is absolutely not a good idea, because every single tiny change made to the files would update the whole thing, and completely kill your bandwidth.
You could also rent a small low powered server, if it's only for two people. You could get one fairly cheap, but it still costs money.