Sorry to hear about your misfortune.
There have been some studies that urge someone with a broken arm to train the good arm as there are neurological carry over to the injured limb. Interesting huh? When you get the cast off your injured arm will supposedly respond faster than if you had not been training the good arm.
Have you looked into any of the old work from Charles Atlas? He used a technique call “Dynamic Tension.” Granted it’s not like hoisting a heavy barbell, but it might be something that you can actually do in your current state which would forestall muscle loss. I think it has to do with flexing and relaxing.
As far as your emotional state, when negative things happen to me (as they do all of us) for no apparent reason, I always get a bit philosophical about it. I truly believe that everything happens for a reason. You may not know that reason right now (or ever) but it happened for a reason!
Who knows, maybe by displaying an attitude of a champion right now you will be an inspiration to someone who really needs it. It’s not always about “us,” we are sometimes meant to help another.
Just a little food for thought.
Good Luck, hope you heal up fast and are back at it!