Heartless — R.C. Martin

He was faithful, until he wasn't.
She was honest, until first touch…
And against all that is pure and noble, they fell in love.

Warning: This is not one of those novels where the characters' actions are justified. It is merely a story about two people--two flawed humans--who fall in love under forbidden circumstances. It is intended for audiences 18+ years of age due to explicit sexual content.