OP here - Thanks for the input, everyone. Highly entertaining with some great nuggets of wisdom thrown in (Looking at you in particular, GrimSqueaker).
Unfortunately, moving out isn't in the cards right now - I'm still in the process of building the emergency fund back up after those months of unemployment. On top of that, I like the apartment and it's all of 1.7 miles from work. Add in my hesitance to move my furniture down 3 flights of stairs again (Ok, that's purely my own laziness, but it's seriously a pain in the ass), and it's just not going to happen.
As for killing our friendship - If you remove the money aspect, we get along really well, and I do genuinely like Jack when he isn't mooching off me. I'm focusing on the negatives and my frustrations, not the good aspects of our friendship. This is the Wall of Shame and Comedy, after all.
Having said all that, I'm not going to let the guy walk all over me.
On Saturday, I was driving home from an event when Jack called me, asking if I wanted to go to the grocery store that afternoon. Perhaps it was a conversation that should have been done in person, but I've been avoiding it and saw my opening, so I said, "Look, man..." and laid it out. I tried to be nice about it, I didn't specifically call him out for being a mooch, but I was straightforward about the fact that I thought food-sharing was weird going in, that I gave it a shot but it wasn't working for me, and that I'd only be buying and cooking my own food from now on. He seemed confused and tried to argue about how well the system had been working, but I held firm.
So expect a bit of a tantrum when you cut him off from using your resources. He might cry, or stomp off, or become pathetic, or act obnoxious. That's a survival instinct, to him: his source of sustenance is leaving, and his first reaction should be something that prevents it from escaping. Just recognize the tantrum for what it is: a test to see whether you're stupid enough to let him latch on again. This is not a test you want to pass.
Woah, GrimSqueaker is psychic!
Since that discussion, Jack has basically refused to look at me or communicate in more than grunts. I'm attempting to be cordial, and he's probably said a total of 10 monosyllabic words to me in the last 3 days. When I'm around, he does nothing but sit there silently and glare at the tv. Obviously playing a waiting game.
What he doesn't realize is that once I draw a line, nobody (with the sole exception of my mom) can out-stubborn me. Good luck trying, kid.
Personally, I'm finding it really convenient to only cook and do the dishes for one person again. I didn't realize just how much of the work I was carrying until I stopped doing it, and I'm loving the freedom.
From the garbage littered around the kitchen and living room, though, it's obvious that Jack has yet to eat anything but frozen pizza, ice cream, and fast food since I stopped cooking for him.
No, wait, wait, wait... that was too harsh. He DID cook a box of Kraft mac & cheese for himself last night. Which he then finished off in a single sitting.
No wonder he's spent the last few weeks bragging to people about how healthy we've been eating. "You won't believe it, we're even having salads most nights!" I wasn't aware that rinsing and tearing lettuce was a complicated task, but apparently it's outside of his skill set?
Will keep you all updated if anything interesting develops from here.