You.must, must start protecting yourself financially.
If tomorrow he ended the relationship and threw you out the house (which he could easily do) could you financially pick.yourself up and easily continue supporting yourself and your children?
If not, you really need to prioritise this.
You have to have savings and a pension
Some people gave suggested buying your own property, which is another good idea.
I know it's tough at the moment financially for all of us. And with 2 children there is always something they need.
But I can't stress this enough, you are in a vulnerable position and you must start thinking of yourself.
The first thing i would is not contribute to mortgage, DIy, upkeep of the house.
He can't argue with you about this because he has made it very clear this is his asset and he is protecting it.
Which is fine
But you have to do the same. You need assets too.
And he is a real selfish dick if he doesn't understand this.
Critically look at your finances and start savings and pension if you haven't done so already.
Even if its £50 a month.
In the long term, should he end the relationship, this money will be your life saver.
At the moment, it's all sweetness and great. But as we've seen many many times, things can end up badly.
And the only person who will be in a shitty position is you.
I hope it doesn't happen, but you need to start thinking what you would do should the relationship end.