Chewy is being REALY agressive!

Ever since he had to be separated from Kenzo because Kenzo got scared when he came near, Chewy has been extremly agressive!
He has never been very friendly to humans, but all he did was hide when we had to pick him up and stay away from us.
Now, no one can get near him! He actualy growls realy loud and steps forward in an "attack mode"!! He growls at all the humans, at Kenzo whenever he's near, at Chiqui (my cat) who he usualy dosen't mind, hell, he even growls at any bird that comes near!!
He bites too! I can't get near him without him trying to bite me!
I am thinking it could be boredom, because Chewy is usualy with Kenzo 24/7, but he has tons of toys (chewy loves toys, Kenzo never cared for toys, he prefers human company) he plays with all his toys and when no one is near him, he is relaxed and happy.
It's just that no one can get near him without him being agressive!

Any ideas why that is? Are there any ways to deal with his bad mood?
Also I am worried that I won't be able to put Kenzo together with Chewy again when he's cured, if Chewy is still that agressive, and that would be a real, big, big, BIG problem.