What I do absolutely agree with is that matters cannot continue as they are - as much for OP'S dh as op & child.
He likely needs medication as well as good quality therapy with someone experienced in dealing with OCD as entrenched and severe as this is.
Unfortunately the bad news is OCD is incurable. Mainly because it's not purely a mental illness but has its believed by many a neurophysiological/genetic component. But it can be treated so that it's manageable.
Although dx almost 13 years ago, with hindsight I believe and hcps and my parents & siblings agree, I've always had it and mum has it to a degree as do a couple of her siblings and when I thought about it gran probably too. I was never a kid that liked playing in a messy way or even with things like sand or play doh.
But it first flared up really badly after dd was born and I was exhausting myself trying to keep everything clean and tidy while recovering from an emcs and looking after dd inc bf.
Hv noticed home was ALWAYS spotless even if she turned up unannounced. She was lovely about it but in hindsight should have been more assertive in getting me to go and see a dr.
As dd got older and reached those stages where they're naturally messy/dirty I did relax a bit. I certainly didn't react how I actually wanted to as I knew that was wrong but for me it was incredibly hard dealing with the thoughts & feelings. As a pp said while the rituals are the obvious things to others, the most difficult aspect for sufferers are the thoughts and feelings.
So many people have said "just don't think about X" I WISH it were that simple.
When it next flared was after I was in a serious car accident which resulted in me being left physically disabled (though that wasn't immediately obvious), car was written off and it was an old banger anyway so actually even with the insurance payout I couldn't afford to get another and I was out in the sticks so this made life very hard both practically and financially and the timing meant this was an incredibly stressful time in other ways.
I ended up having a full on breakdown and crisis team were called in and they were seeing me daily for weeks.
I've since had periods of wellness, and periods of where I'm really ill again but not quite as ill as then.
I've had several different medications - some have helped some have made things worse (but often you're urged to persevere - and some do take several weeks to start working) it's very much trial and error unfortunately.
I've also had several courses of therapy and at one point got to being quite well again - unfortunately that therapist has now moved out of area. That's just life and bad luck.
I'm currently housebound agoraphobic because of it, trying yet more new meds, cpn seeing me fortnightly (would be more but cuts mean local Cmht is understaffed and has been for some time now) and honestly I'm so sick of feeling like this.
I'm not at all saying that raging at op and certainly at the child is at all acceptable and if op feels the need to leave as a result of this behaviour that's understandable.
But there's a sense on this thread and on others regarding mental illness that somehow the person who is ill is choosing to be the way they are.
Nobody chooses to feel constantly anxious, to question every action they're about to do or have done repeatedly, to fear simple acts of everyday life like putting something in the bin to going to the toilet to making a drink.
Most people have a fear if not a phobia of something. Try and imagine if the cause of your phobia was something you had to encounter every time you had to the simplest of daily tasks.
Eg if it's spiders imagine every time you had to turn on a tap, or sit on the loo or put something in the bin you had to touch a massive spider. That I hope gives some idea of what it's like.
Most people can avoid their phobia to a degree. It's much harder when the thing you fear is basically everywhere.
Op I'm so sorry you're dealing with this, you sound very kind and understanding but also absolutely understandably frustrated and concerned for the effect on yourself and your child.
Has his mum never tried to get him to see a dr about this?
I wonder if an intervention by not just you but also others like his mum, maybe your hv, might make it harder for him to deny the issue if 2 or more people are saying to him "this isn't right you HAVE to get help".
While medication is not the only thing that should be used or that will help it can, if he's lucky enough to find one quickly that works for him, be very effective in much reducing the anxiety.
I am more than happy to discuss further via PM if you wish.