It turns out that I didn't completely tear my left ulna collateral ligament. This is good! Instead, I completely tore my left radial collateral ligament. This is bad, but much better than tearing the UCL. If the UCL is torn, the only repair is surgical, because the ends can get pulled apart by the muscles in the webbing of your hand and be trapped. I am probably not going to need surgery, because RCL tears can heal more like a bone would--if the ends are close together and immobilized, they'll "grow" back. There aren't bones and muscles in the way.
So now, I am in this for 4 weeks, at which point I'll be starting PT or being scheduled for surgery. I'm rooting for physical therapy.
The new splint is hard plastic and I can clean it with rubbing alcohol. This is a good thing!