It's worth pointing out that men gain an enormous amount from marriage/stable relationships.
So, when posters talk about 'bargaining power', as though the woman has won the lottery when she marries some man, it's not the whole story.
It's been shown that men get promoted more when (other men) see them in a stable relationship, especially one with children.
Men's health and well-being increase measurably when they're in a relationship, long-term.
Society rewards men for being in marital or marriage-like relationships.
You, OP, have conferred all those advantages on your partner.
And you've facilitated a relationship with his children.
All those advantages disappear if the relationship goes bang.
Especially the health and happiness one. (This is worth remembering. If he does screw you over when you get serious with him, you can comfort yourself with the thought he will get sicker sooner, and die earlier. Statistically.)
So, the cards aren't all his.
A long-term relationship/marriage isn't a bargain whose terms you set in stone in the first months. It's an ongoing thing.
Right now, you are creating a really great life for him.
It's a big deal if you turn round and say: 'This is great for you, not so great for me. Things have to change or I'm taking it all away.'
Never, ever underestimate what you are bringing to this relationship.