I’m staying with them for free right now.
You've said he's there if something goes wrong, so is he coming with you on outcalls? If so, I'd offer to pay him something for his time and travel costs but it would be a flat rate, not a percentage. If not, then expecting payment just for being somebody's security buddy is a really shitty way to behave.
If you're staying at his place I'm assuming you don't live within easy travelling distance from the bookings you're doing? In that case I'd expect to contribute something towards food and bills, but again it would be an agreed amount regardless of how much you've earned, just as it would be if you were still working in a restaurant.
Basically, if you're being treated differently than you would be if you were a hairdresser say (or any other job), he's taking the piss.