Sorry essbee, missed this. Just wanted to add my two penn'orth. I think coming up to 6 is a very difficult age for boys anyway, they do a lot of changing, and re-assessing their place in their universe. I've posted here before about my problems with ds1 - how I feel he is growing away from me, resenting me etc., and my ds hasn't gone throught the trauma and upheaval that yours has.
Ds1 has changed so much over the last year - I sometimes get flashes of my sweet little boy so I know he's still in there somewhere but he can be moody, aggressive, destructive, sulky, sullen and downright unpleasant much of the time. He also seems to have more time for his Dad than for me right now. I read Steve Biddulph's book "Raising Boys" and, while I thought a lot of it was pants, one thing he said rang a lot of bells. He says that boys are their Mum's til they are 7, their Dad's 'til they are around 11/12 and then their world is dominated by peer pressure 'til adulthood (when presumably they find their own way )
Perhaps your ds has mixed feelings about his dad going - despite his assurances that he is glad he's gone. Perhaps he is feeling he needs a father figure - though your ah isn't the one he needs. Does that make any sense? This isn't an instruction to rush into finding a replacement btw
You are doing the best you can - I don't think there is a quick fix. You need to keep the channels of commununication open, keep hugging (when you are allowed!) and I agree with a lot of what monkey has said re: acknowledging that it's OK to feel angry and full of rage. Boys are very testosterone driven - they have a lot of energy which they need to channel somehow. Could he do some kind of self-defence type thing: judo or karate? I've been thinking of something like this for ds1: I think it's a really good oulet for all that energy and a great boost for self-confidence.
He is still your little boy though, I really do think he is testing the boundaries and finding out where he stands in the new scheme of things, and I think they all do it - but you've had a lot happen over the last year or so to make the transition even harder.
I also think the bullying is bound to have a bearing - if he feels powerless at school, he may be inclined to exert power himself at home, wher he knows he is on safe ground. Definitely go back into school after Easter and insist they pull their collective fingers out!! Ds1 is quite matter-of-fact about the bullying (mild, more of a teasing kind of nature thankfully) that goes on at his school - his attitude seems to be "well, that's life, and it's OK, I can cope." But our kids shouldn't have to cope with anything worse than that.
HTH a bit xx