For the kids,
Does it really benefit the kids? What atmosphere are they growing up in, what dynamics are they seeing? Would you be happy for them to recreate this relationship in their own futures?
for the wider family,
Family get used to change.
for societal norms,
It's not the dark ages, divorce is normal.
for the buffer against old age loneliness -
Like I said above, is he actually the guy you want to spend old age with? He's not going to get any better company. Is retirement with him going to be fun and time well-spent?
And if your or his health deteriorates, do you see yourself being his carer or cared for? I'm seeing a lot of older couples in my life where there's dementia or cancer etc. It's hard, it's devastating and it's one thing doing all that caring for someone when you love them and had many happy years, but if you've just tolerated each other ...?
And men tend to die earlier than women, so hanging on will probably still mean you spend your last years on your tod.
and be happy. Please tell me I won’t be alone and it will be okay?
Being single can be happy. What's so awful about being on your own?
And he is not the only man in the world.
You get one life, OP.
It's up to you what you do with it.