husbands ex... and their child

My husband has a child with a girl that he cheated on his former-fiancé with.  She magically got pregnant like- a month into their time fooling around.  Yet we have been trying for months and it bothers me that so far- it has been to no avail.  I also feel like he won't love our children like he loves his child with her because he does everything for her and their child and would sacrifice anything to make them happy- including me.