I just replaced mine on the driver side a couple weeks ago. Same thing happened to me. I would hit the brakes, it would pull to the right hard, then straighten out a bit. Once I got off the brake, it would pull to the left and the wheel stayed warm. I replaced the hose. I did have to clean up the threads on the flare nut, though. I carefully ran a die over the threads because it wouldn't thread into the new line. I had never heard of this before, but ended up replacing both sides anyhow and had to run the die on both sides.
To verify the hose is collapsed, you can push the brake to where the wheel is locked up, then release the bleeder fitting. If letting that pressure off lets the caliper release, then it's a hose. If it's still tight, then it's a caliper.