It's hard because I don't want to ever be in the situation where I'd have to tell him 'no' and the possible outcome of him being angry with me. I don't have another parent to go to. I'm more fragile than I come off as. So... How can I be supportive of him... but keep the boundaries?
Ooh man, this one hits close to home. I had similar kinds of abuse growing up. I became the little adult. You don't have to be the parent. Let your dad be the parent. Let him be supportive of YOU. My dad got better and better with time. While we invariably hurt those we love, mostly we/they don't want to and don't mean it. And then we grow.
There is a bright future with your dad, one you missed growing up, & with the power of goodness, it will allow you to be the nurtured daughter you are and were meant & deserve to be.