Many birds only bond to one person only, and some are just love everyone. I would suggest to put him in the cage for time out when he attacks your partner. Your partner also needs to stay calm and to not get scared. They sense 'scared' and they use it to their advantage, I'm sure of it!
Both mine are completly different personalities. My eldest is friends with most people he sees regularly and 'gets to know', hes shy at first interaction, but by the 2nd or 3rd time he sees you, he decides your a friend. 'Lola' on the other hand, is almost 2 and
only likes me and Jibby, she still flys away from my partner and any visitor to our house.
Maybe they see your partners as 'threats' or competition. I'm sure Lola hates it when Rory (my partner) is spending time with me. She puffs up and does this annoying screetch. But then Lola is possessive of most things she 'values'.. cage, food, Jibby, me etc... and puffs up if anyone messes with 'her stuff'.
As far as I can see, my partner does nothing wrong and does try to offer treats, to no luck. Maybe its something that bothers them that we cant see? Like the tone of voice etc.
I think we just have to accept they will not get along with everyone. All we can do is try and 'discourage' bad behaviour.
