Is this our life-long duty?

[notnownorma]

DH is very firm that we have a "duty" to support our disabled adult child (living independently but struggles to stay employed) financially for the rest of our lives (and then leave enough for them in our wills) as it should not be up to the state at all. We've claimed in the past as I wasn't able to do paid work but child now qualifies for very little.
I get that benefits aren't great, happy to supplement for big ticket items, holidays, unexpected bills, I would not see them go without essentials, but supporting them completely would take all our spare money including savings, leaving just enough for a very basic lifestyle. DH is happy with that: he's not interested in travel, outings, entertainment or outside interests except his very cheap hobby and church-related social life.
I'm not. I spent a lot of difficult years and would like some fun now. AIBU?

No, you don't and it's not the best thing for your adult child either.

He is setting them up to a massive change when you two die (probably worn out after a grim retirement) that will be hard for them to cope with.

Get all the external support you can, including benefits etc, in place now.

Your DH sounds like a very committed parent. But, it does seem unrealistic to expect you to live the rest of your lives in a very restricted way to care for your child.
If your child is struggling in employment and needs to rely on benefits a starting point is to ensure they are claiming everything they are entitled to. Also what could help your them engage with work more successfully. With help many people with a disability can work, even part time makes all the difference in the world.
In these times many of us can't shelter our children from the hard reality that life is expensive. Budgeting and making choices carefully is what there is. Independence is really valuable , and your child may struggle to reach their potential if financial support at a high level is always provided.

Agreed with @DisforDarkChocolate.

Sort out benefits and care support that you can for now. Maybe life insurance policy for when you two die, and someone to administer it via a trust? You can’t be sure what your own care needs might be, your savings/property might have to go towards that.
whilst it’s nice that you can support them and want to do so, you also need to enjoy your own life. There is a balance via compromise I’m sure.

Agree with previous, help your child claim everything they are entitled to and enjoy your own life too

We are faced with this with DD (who is just a teenager ).

What happens when any money you leave your child runs out?

You owe it to your child to help be independent so they’re not reliant on you when you’re no longer here.