I like where this story is going so far!  As far as where I like to take the story, I personally would like if Tiffany was just acting aggressively because she loves him and does not know how to deal with it and is trying to get him to love her back and that his family and friends are dismissive of him because of his small size and wants to be with Tiffany.  Also concepts like breastfeeding because normal food is hard to digest and insertion not just for sex but for protection, a way for Tiffany to keep him safe and store him while doing things.  Basically a loving giantess where the little man is reliant on her body for protection and sustenance, and the giantess herself for love.  I don't know how much of this is compatible with your story but please keep up the good work and feel free to use any of these ideas.