I can see in my email you left a post, but I can't find it in the forum anywhere, I am going to attempt to answer your post (I can see it from my email). Once parrots start screeching it has become a learned behavior. It takes a long long time to unlearn these unwanted behaviors. It takes patience so much patience sometimes you feel like you are going to start screeching yourself. Reward his quiet behavior and IGNORE the screeching; the unwanted behavior.
Try music, television (stay away from nature channels) get a couple of those rope toys with blocks and stuff, where they spend hours unraveling the strings. Give him stuff when he is quiet. Turn away from him with your back to him if he screeches. They need a lot of toys to keep them occupied.
If you leave the room and he screech, if you have to return during the screeching, return, in mean (but calm) voice say bad bird, and turn your back to him, ignore him until he is quiet.
Do either of you sing? Sing to the bird, he will love it. Sing childrenï¿½s songs with limited body motions. Just close to body stuff, no outreached arms, and such. If youï¿½re happy and you know it clap your hands. Things of this nature.
Will your boyfriend spend time with the bird? Does he like the bird? If he does and will spend time with the bird, have him spend some quality time every day talking softly, giving treats, try to stay out of biting distance but donï¿½t show fear. There is a reason he or she doesnï¿½t like men, someone was cruel at some point in time. Get some cool toys (just cheap Kool-Aid colored safe wood blocks from a lumber yard. Just make sure there are no chemicals on the wood.) They love to disassemble stuff. Have your boyfriend give him these special toys (only if the bird is behaving).
Keep that bird busy. Only cover for short periods of time during screeching episodes, or just use theï¿½ I am unhappy ignore him with back to him methodï¿½ instead of covering. Cover at night to give him 10-12 hours of dark sleeping time though.
I hope you can stick with it; it will only get worse if you have to give up on him.
It will take time. These birds have the intelligence of any human. Once a child has behavioral problems you know how difficult it is to undo these behaviors.
Did you go to the vet and what did the vet say?