The following books are romantic standalones. In each book, the couple gets their happily-ever-after, but the series plot continues with a different couple.
The Feldman Brothers Duet
His Brutal Game
His Twisted Game
The Marked Blooms Syndicate Series
The Afterglow Series / The Dahlia District Series / The Adler Brothers Series
His Pet / His Pain (timelines overlap)
The following books are standalones. They may be read in any order.
Dreams of Glass