@Bluefairy00,
I think that you know your answer.
He works hard, he's intelligent but no so intelligent to not file taxes, but intelligent enough to live with you, get fed, washing done, meals on the table, all free yet, happy to make sure the kids have a large TV, happy to kick you out on Mondays and make you walk through the dark, happy to let you work, run a business and do the whole lot yourself, whilst feeling guilty that you need to help also with paying for his kids.
He's not ready for a relationship at all, probably harbors bad feelings towards his ex wife, non trust in relationships, maybe deliberately doesn't pay rent and runs his business at a loss or nearly, to not pay maintenence I mean how can he work hard, be intelligent and not have money? Unless that's deliberate.
I'm sorry that you weren't able to have children or may not be able to but that doesn't mean that you need to settle, have some guy live with you free and do nothing. Who is to say it's too late in any event, it will be in 2 years time if you don't kick this guy to the curb and find a more suitable partner who respects you, contributes to your life and "lives in his own house".
Off course he wants his kids over, that's natural, they are blood.. The kids love their Mother and grew up with both of them, it takes time for children to accept another lady in their Father's life, nothing to do with their Mother being alone.
And again, he works so hard, intelligent but business doesn't make any money are you sure?
Maybe that's the reason why his wife and himself aren't together. Maybe he is a dreamer and not a doer .. But he's using you.