Firstly and understandably your experience with your ex is going to make you feel more vulnerable and maybe take to heart the nasty things he says potentially more than if you hadnt been through that experience in the past, so if you can, try and separate that it might help you, because despite his current behaviour he is not your ex, and his normal behaviour before this happened wasnt abusive and as Sandra says it isnt your fault -he is the one lashing out and he has temporailly changed but this doesnt necessarilly mean a permanant change.He is trying to deal with grief and getting into a cycle of feeling drink helps which in reality it doesnt because its a very temporary fix which then adds to depression.
Its very early days and often people disapear from your life after the funeral leaving you to deal with the aftermath of emotions,guilt,anger depression being just three of the more common ones, but also sometimes there is a defense mechanism in our brains which tells us we wont get hurt again if we dont love other people - so we can try and put a barrier up and push them away - this also passes because of course we cant just cut off love for other people especially not our children, but this isnt a rational journey,so maybe he is subconsciousely trying too do that with you.
Secondly his drinking is a form of self medicating,rather than facing his emotions so its likely he claims he feels better on a night out because of that, rather than because of being with his friends.Alcahol is a depressant and he may feel better at the time he is drinking it but then feels worse when it wears off and unfortunately thats when he gets home to you - there is also a physical element too it more pronounced with him because of his diabetes -alcahol is loaded with sugar so he will be getting spikes of sugar which quickly drop and that also creates massive mood swings.I have seen normally nice people with diabetes turn into some-one completely different when it gets out of control - they cant help it, its nuerological but it can be devastating for relationships.
I agree with Ems try and get him to spend more time with the kids -take them to the park - for picnics -or days out, then build up to weekends away later because a weekend away right now might turn into a disaster, he may feel he shouldnt be enjoying himself for a whole weekend - its the illogical guilt thing that happens pretty much to everyone the first time we laugh or do something enjoyable,so for now shorter time gaps may well be better
The friends that have noticed and are concerned could maybe help by arranging to do things other than drinking - a lads day out, go- carting or laser shooting, or something more adventurous, white water rafting,climbing etc (within the boundaries of controling his diabetes of course) - Being outdoors is always a good healer and physical activity a good way to expend pent up emotions we might otherwise try and drown in alcahol.If he isnt into physical activity then a day fishing can be therapeutic i,m told. Anything that will take him away from the pub and help him realise he doesnt have to go there to be with his mates and he doesnt have to drink to feel better even temporarilly.
Telling him not to drink but then not replacing the solace he perceives it is bringing him, with an alternative is less likely to work, than putting something in place which gives him less time to drink and an alternative more healthy means to self medicate ,so he feels less need too and hopefully slows down on it himself though his own choice rather than being told not too.
Also i suspect he may have attracted some hangers on who see an opportunity to carry on drinking back at your house rather than concern for his health and relationships so maybe less time in the pub means he might drop some of the not so good mates who may well be encouraging him to stay and have another.
meanwhile take what time you can to be kind too yourself and have that time out even if its just a long bath and candles or a good bookk/film or even something mindful like colouring books because you need to keep up your strength and look after yourself if you are going to be able to help him.