Does Deku ever get healed?

no, the little girls power healed him during the raid…. It’s possible it was due to the effect of his dream, though if you look closely when Deku is battling Overhaul with Eri’s help his scars disappear after he defeats him.

Why does Deku keep breaking his bones?

I was thinking about it and I believe the reason Deku keeps breaking his bones with OfA is because his full cowl only covers his muscles. I believe he isn’t infusing OfA into his bones so his bones aren’t strong enough to withstand the force. It doesn’t make sense for every other wielder to not have this flaw.