Mayissa,
Sounds like you are doing everything right on your own, but you need the help of a
excellent behavior trainer. (not just an obedient trainer)
For now, keep using the muzzle,
not only to protect others but to also
protect your dog.
You did not mention if he was neutered.
If he is not, I highly suggest you do it as soon as possible. Do not use this dog
for breeding.
I applaud you for what you have done
on your own.
Please keep us posted in the future.