Since you are not his wife, so you can't 分割財產, if you divorce with him, he will or you will pay child support, it depends on who will have custody. And also, since you still remain your old marriage, so once you break with your BF, if he use this to attack you, you would get in trouble.
Don't dream that way, unless you don't care his money, just love him, otherwise, you would get punishment, sorry for my straight.