family changes like this can be unsettling, especially for a 14 year old.
there will be all sorts of emotions as well as teen hormones bouncing around. and as a teen boy, he will be acting tough about it.
im not saying by any means that this is an excuse for his behaviour.
have you tried talking to him, when he hasnt got mates round and he seems quite calm, just try and talk, tell him how he is making everyone feel.
i dont know what sort of relationship you have with him, or how long you have known him, that could be a factor.
xxxx