Interesting that there are more replies telling DH to chuck rugby than there are for SS's mum to quit partying on a Friday and dating unsuitable men! (Just an observation)
What good would those replies do? OK, she's a mentally unstable alcoholic with shit for brains. Nothing we can say or do will transform her into a good parent or stop her destructive behaviour. But your DH is (supposed to be) a responsible adult who cares about his son and his wife. So he is the one who has to step up.
Agree that DH should skip the odd week of training but not that he should chuck it all together.
At first I was going to say: Well fine, then why doesn't he just do that? Why can't you tell your DH that in fairness to you and to his DS he needs to skip the weeks of rugby training while your family are visiting?
But then I read about the broken arm and the suicide threats and this:
A child whose mother commits suicide over the child's custody isn't necessarily going to be better off than if he stays with her and she gets support.
and my head exploded.
The ex is not getting real support is she? Because the boy's father has not done anything about the physical abuse of his son or the suicide threats. He hasn't gone for full custody or involved social services, so how would the support services have any idea all this horror is going on? Most of the time the boy is just being left alone with his mother in her unstable mental state and with her violent sex partners and drinking companions.
OP, what a wet lettuce your husband is. "Needs to blow of steam" ffs. What he needs is to man up. Not leave it to his 10yo son to care alone for his mentally unstable alcoholic mother. And not leave it to you to care for the son while the father goes off and plays games like a little boy.
You and your DH really seem to be in some kind of denial and minimising how shocking this situation is. This isn't something he can paper over with money and private schools and deposits. Or even that your good intentions can paper over by helping his mum out. It's way beyond that. Your DH hasn't reported, hasn't taken steps to remove his son, is complicit in all the horrible physical and emotional damage that must be happening to him while he lives with his mother. Tell your husband to wake up!
Ahem. I will now calm down and scrape the bits of my brain off the walls.