I see a few other threads like mine, but no one has posted their log file, so in hopes of fixing this as soon as possible, I'm making my own thread.
here's the log paste: https://pastebin.com/xhV2jexC
I tried installing the latest forge build (14.21.1.2443) but whenever I press play, the launcher closes for a second, then reopens with the message: GAME CRASH An unexpected issue occurred and the game has crashed.
I thought it might have been a bug in the newest build, so I after that, I tried installing the latest recommended build (14.21.1.2387), but I got the same error message.
Both the vanilla release of Minecraft and OptiFine 1.12.1 launch and play properly.