Aww yeah. I see Theo only calling him Matty when he's being really affectionate... So I don't know if you noticed, but in my writing I only use Matty when Theo's feeling affection towards him. Where as he's usually only described as a witch when Theo's pissed off, as it comes off more insulting.
And I just had that same thought of maybe introducing more characters. I could see Theo having a werewolf friend maybe and perhaps him or someone else could die off