as a lot of others have said, he really could benefit from proffessional counselling but at 16 thats going to be a difficult thing to persuade him to undertake. When parents split up it often has an understandably drastic effect on kids and their inability to verbalize their feelings ,confusion and hurt often leads to anger out of sheer frustration. I know my lad (at heart a very placid and generally "nice" young man) went off the rails for a while and nearly got expelled from school ,trouble with the police etc but it all-luckily-turned out well in the end. Its because , whatever the situation, kids tend to want mum and dad to stay together and they arent mature enough or worldly enough to understand the reasons why things happen between people. Try and persuade him to see someone who can help him deal with his anger and frustration and try your hardest not to slag his mum off in front of him however hard that can be and however much of a cow she is to him/you. You are the adult so you're the role model so you are the one who has got to try to be seen by him to be reasonable in your attitude to things including her actions. Make him know that you love him and will look out for him but also let him know that certain behaviours are not acceptable.Spend quality time with him as youve said like going to the gym so you can better bond with him. Like all kids-esp of that age!_he will push you but he will do that to sort of test his boundries as well as you. You know, the old will dad leave me too? what if I do such and such, will dad kick me out. Its a very fine line and it certainly aint easy but if you can be firm with him but still reassure him then you'll ultimately be the closer for it. Hope I arent "teaching you to suck eggs" or anything but as someone who has merged 2 families together(much of the credit due to the patience and maternal instincts of my better half I must say) I know a little of what youre going through. It'll take time and it wont be easy but you'll get there. (oh, btw, this is a need to know situation so school/college/work need to be kept informed so they can understand reasons for your sons sometime aggression. My lad wouldnt initially respond to me or his teachers but he did respond well to his young mentor they put in place at school).Best wishes mate,especially at this time of year which should be all about you and yours