Take it slow after your cast comes off. Just because the cast is off doesn't mean you can go trying crazy shit and think your arm is going to take it. Usually when a bone is broke it takes 8 weeks for the bone to heal enough to take the cast off. In that period of time your muscles atrophy (weaken) thus when you fell the second time the muscles didn't support your still weak bone and fractured again.
Which bone did you break, Hurmus (large bone in your upper arm) or one or both of the forearm bones Radius and Ulna?
You'd be smart to strengthen the arm as a whole your wrist, forearm, biceps, triceps, chest, shoulder and scapular muscles as these all weaken due to lack of use secondarily to you being immobilized by the cast. Start w/LIGHT weight and progress SLOWLY. If you don't know how to do this safely, seek out a licensed, professional trainer or physical therapist like myself. You may only need to see them once or twice to get the basics of what to do. Good luck don't do anything stupid!
My reaction to first snow fall
2012 NS Legacy 163.
2013 NS Brothers in Arms Cobra 163.