Some people just don't believe in marriage. I started off thinking, who's to say that just because he doesn't believe in marriage that he is not 100% invested into this relationship, that is heart is not completely in it.
But, then I got to the end. I'm not sure. You got pregnant accidentally, when the two of you were not really in a relationship anymore. Do you think you would be together if it weren't for your son? He realized he loved you, but you wanted out... I'm assuming your feelings have since changed?