Eliza, I think your DS choosing his own flowers in a Dad shape is a good sign - an emotionally mature thing to do for an 11 yo to recognise the different connections in his dad's life. One of the things I have read about childhood bereavement is that children can blame themselves (wholly irrationally), that if somehow they had been 'better' this would not have happened. Perversely, if your son's behaviour at school or home deteriorates, this could be a good sign that a) he is releasing some emotion and b) he feels in a 'safe' enough place to do that.
Your friends might be struggling with ExP death - there is a natural instinct to view the history of the deceased through rose tinted glasses (seems like EXP family are taking that to the extreme). Maybe your friends are protective of you and DS. If they know the history and cannot think of anything decent to say, they think silence is better than speaking ill of the dead and all that. But still, however useless he may have been, ExP was still your son's Dad - so like I say, flowers conversation is a good sign.
I am sorry if this offends you, but you should prepare yourself for people thinking/saying that the death 'was for the best' for your son, given the history. Completely ill informed and inappropriate but I'd be surprised if it didn't come up.
Chipping, Thanks, DD's treatment is going ok, some days are better than others. We've a long way to go but she has a BIG personality and that seems to be carrying her through. I don't think she really gets that her friend died. DS on the other hand initially couldn't understand how friend's parents were still alive, if their son had died. He also said he hadn't seen me cry, so I can't have been sad. So me being upset kind of gave him permission to be. Seems to have more understanding now, although he told DH that he (DH) can look forward to getting old 'because he will become a grandad and he'll be really old so he will be nearly dead!'