This story has been running through my head since I read it... every part of it is really horrible.
The two things that occur to me are that first, as much as it sucks, you should not bring another pet into your home if you can't keep your step brother away from it. As a teenager, you might not have much choice in the matter and that royally sucks. But eventually you'll be living on your own and will be able to choose who comes into your house and who doesn't, and then you can get another pet.
The second thing that occurs to me is that your step brother sounds like someone you want to be careful of and shouldn't be alone with. An adult in his 30's who would do something like that to a teenager has problems, and could be potentially dangerous even if he is (or says he is) getting help. It may be hard to imagine something bad happening, but people are injured and abused by family members every day. And the fact that he would do something like pour boiling water on a living animal just to spite you (or use his own pet to play a trick on you) just reinforces what he might be capable of. So, be careful. Don't be alone with this guy.
