and as a follow up before someone says "But he has depression" or something; HE NEEDS HELP. The character needs to get his act together an get help for his depression because he is currently a care giver FOR A CHILD. If he can't then he should find someone that will take care of her and then he can do whatever he wants and let himself heal at his own pace. But as long as he's taking the responsibility to take care of his kid sister he needs to pull himself together. Or, like I said, dump the responsibility onto someone that gives a shit. She's a growing child and needs a stable environment to grow up in, not someone who is not only depression but prone to violent outburst. Yeah, this is not a safe environment for her to be living in, regardless of the reasons.
I figure that this is his way of cooping with the loss and / or he blames his sister for the parents death, but why does he have to be such a major asshole toward his sister? Seriously, she's a child and his sister that he once had a good relationship with, no matter what happened to him she's not going to understand unless he puts it into words. HITTING her it NOT that. Honestly he's just being abusive toward her at this point. (and unless he has a VERY Good reason for being an asshole all this time I don't think I can ever like this character)