Why has my son been doing this?

he is 16 years old. he is usually a very good kid but he hasn't been lately. well the first thing he did was end up in the hospital because he drank over a half gallon over whiskey and i gotvery mad over that but i let him off the hook after a week then a cop showed up at my door because he had broken into someones house the cops let him off the hook with a warning but i didn't then he told me off and ran away for a night. then he seemed to stop with all of it, so his cousin brandon came over and i heard some loud noises so i went in his room and alex (my son) was beating on brandon, he was right on top of brandon punching him in the face and stomach so i pulled alex off him and brandon was crying so i took him and cleaned him up and asked what happened and he told me that alex was trying to get him to smoke and he told him he didn't want to so alex just jumped on him and started attacking him. they usually get along very well. and now they haven't talked to eachother and alex is hanging out with this kid named issac and they sit and drink together and smoke. now alex is wearing all black and painting his fingernails black, and wearing fingerless gloves, and painted his hair black. what is going on i didn't raise him like this, what should i do?