Honestly, move out. The last thing you need is to be stuck in an environment where there's no means for you to, well, grow up and move on. What are the "expenses" that they've had to spend on you? Is it stuff that they didn't have to spend but did anyway, or important things that you need? If that's the case then, well, you shouldn't *have* to pay them back to begin with. If it was the former, then, well, he should be satisfied with you continuing to pay them in a different form other than rent.
And honestly, if he can't respect you wanting to go out on your own, even if it is to live with your brother, then it's not good parenting. Sure, no parent wants to "lose" their kid, but at the same time if he's only keeping you around for the investment that you provide, and not any actual reason that pertains to your well being, then he's not exactly in the right. And the fact that you fear his reaction might cause harm, is all the more reason for you to have to get out of there.
Sure others probably won't agree but I've seen these quite a couple of times, and usually the people ended up staying until it was too late, and it caused more problems down the road.