Some drugs turn people into monsters - especially coke and crack, whilst heroin certainly makes people do things they wouldn't otherwise just to get a fix, although I've never known herion to predispose people to cruelty to animals. In a way I can feel sorry for him insofar as it is all too easy for the susceptible character to become addicted to certain drugs, especially when exposed to them on a regular basis, and especially when they have the money to support such a habit. I've had friends who have gone down that road and it is sorrowful to see.
I totally agree, however, that the cat and kittens should be removed. I once had friends who smoked weed pretty much all the time, and they had two kittens who they loved to bits, but they would think it funny when the kitties found 'blims' on the floor and ate them and got high. Trouble is, with 'druggies', they are so enmeshed in that world that they think animals enjoy the hit as much as they do.