Are you getting desperate in your old age that you'll settle for being treated with such disrespect and being used as a cash cow?
How do you love a man who thinks you 'deserve' to be treated like this by his kids?
How do you love a man who has ZERO respect for your opinions and feelings?
How do you love a man who tries to dictate your self worth to you?
Healthy relationships thrive on COMMUNICATION.
He REFUSES to communicate on an issue that affects YOU....and you're going to marry him?
You have SEPARATE finances - that means HE pays for costs incurred by HIS children.
So yes - he SHOULD be topping up your joint Spends account to make up the difference that has been spent on his children. Or don't pay for them out of this account.
Not until you JOIN finances should you be EXPECTED to pay towards his kids.
What happens to joint savings and the marital home if/when you do that?
Is he going to expect you to leave your share to HIS kids?
Is he going to ensure that your home ownership/wills are going to be fair on YOU?
What if he dies before you and the kids inherit half the house?
Will you be happy with them moving in/forcing you to sell/evicting you?
Mind you, the kids could move in anytime - are you happy that your views and thoughts on this will be totally irrelevant?
Are you happy that you will always be treated like you don't actually matter unless it's regards money and sex?
Sounds to me like this guy has found a woman to leech off, who will not only share the costs of raising them forever, but will also share the 'parenting' so he doesn't actually have to put much effort in himself.
He doesn't actually give a shiny shit about your views and feelings, doesn't have enough respect for you to DISCUSS parenting issues or issues that are and will affect you.....but he does expect you to keep paying out and putting up.
Some 'man' you have there OP.