Casual/Fling Leads to More (MxFuta)

This is one the very very few things traditionally a little outside my preferences, but decided to give it a shot.

The story is of a boy/man.  One who does not consider himself gay/bi.  Maybe curious.  But in a different way.  This is a three gender world.  A world where futas are another option.

Im flexible on the ages here, teen-early 20s.  Depending on the age, maybe the boy tries someone from school or neighbor or someone.  Someone he is has interacted a little with.  But not a friend or anything like that.

If a little older.  Maybe they meet at a party, or through dating/hook up site.  Whatever the case may be he is looking for someone he can fuck, but who can also fuck him.  It starts as something more casual, but they hit off well enough they decide to keep meeting.  See where it goes.

Looking for good and long story/sex mix.  Some sort of relationship forming.  The guy exploring sexuality to a degree.