But there is a big gulf between abandoning an ill person and that person making someone else a shell of themselves.
Would you be ok if DS stayed in the relationship you are in? With seemingly little impetus from partner to get better, making DS feel like he couldn't talk to them, or had to leave the house?
And have you asked H how he thinks this affects his son? Doesn't he want to do everything he can to be a good, or just better dad? Go out, smile, love his mum?
I would sit H down, and as much as he won't want to hear your side you need to tell him. That you are tip-toeing around him, worried if you say the wrong thing it will set him off, that family life is splintered with little joy, that you feel sometimes your only open is to be out of what should be your home. That home, with your husband and son is not a santorary. It doesn't have to be an argument, it can be approached with love and care in that H is missing out on so much life. Your son will only be 6 for however many months, then only 7 for a year. How much time is going to pass when H can't even say "hey babe pay rise that's great".
Personally I wouldn't settle for anything less than H being fully determined to get to the root of his depression and doing everything, everything, he could to overcome it. Which would include a full on overhaul of sleep, food, alcohol, exercise, time in nature, limited doom-scrolling/screens, medication, therapy, me being able to say when he was being a prick without some sulky meltdown. An acknowledgement from him that it isn't easy for anyone not just him.
Buying a present a couple of days later just wouldn't cut it.
There is a fine line between support and enablement sometimes. And he has a 6 year old son who needs him, if he won't do it for himself or you I would expect him to do it for his son.
That would be my approached. Tough love basically.