This might cheer you up - bones heal, chicks dig scars and glory lasts forever
If the xray is so inconclusive, the two things to take comfort from is that they've decided that you have broken it and are treating it promptly, and that it isn't a spectacularly bad one.
The worst of the hurt passes within about 72-96h with a straightforward ulnar or radial fracture IME.
(One of the times I broke my right arm in a session, I *knew* it was broken (familiarity with the sensation, plus crepitus...woo..) the hospital had a Dr. Nick Riviera actalike on duty as the radiologist the next day and they missed the frac site. Two weeks of climbing around and swimming on it and wondering why I couldn't take my bodyweight without screaming like a cissy, the hospital phoned and said yes, on reviewing the films before they were to be chucked there was a break, after all. )
As for MA training with the cast on, I doubt they'd allow you because one of those things can be brutal, even if you don't mean it to be. If in trouble again, then use it to your advantage.
The other thing is that the bone will heal to be stronger/denser at the fracture site, which can create a problem because to either side the bone remains the same, and is thus relatively weaker. Beware of that!
In terms of training, even over weeks you'll lose muscle in it, compared to the good arm, so if you do train the other one up, it will enhance the difference between the two.
You're probably going to have the cast for three to five weeks, and then it would probably take an equal amount of time with rehab.
Ffs, don't do what I did, and within 48h of getting a cast off, and doing in the other arm by arguing with a grappling hook.