This is the second book in Jenna Kay Francis's Vector series.

Though Baris is a vector he has been able to find a lasting
and mutually beneficial relationship with Anika, or so he 
thinks.  Anika is part of a clan of witches that are also
bleeders.  Since the Vectors need blood to survive, with 
the thanks of Rhiannon a clan member the vectors came to
a mutual agreement.  The Vectors relieved the clan members
of the surplus of blood they built up that would kill them
and the Vectors no longer had to hunt for their survival.  

Baris and Anika had done much more then have a mutually
beneficial agreement they feel in love and married.  The
marriage had gone on quite well until now, when all of 
the sudden Anika no longer wanted to be with Barris.  Due
to Anika's sudden change of heart and erratic behavior Barris
decided to find his friend Vail to hopefully find answers to
these changes.  Deirdre a friend of Barris and Anikas' offered
to go with Barris and being she too was of the clan and a bleeder
as well as wanting a change of scenery amongst other things.  
Hesitantly Barris agreed in the hopes that between them they might
find a reason for Anikas' behavior.  

What Barris found was betrayal, betrayal by Anika when she rejected
him and betrayal by Deirdre when Barris found that Deirdre wanted
much more then a friendship with Barris.  Over the journey many 
things happened, Anika disappeared, Barris and Anikas' son fell
ill and had to be left in the Lair, and Barris eventually succumbed
to Deirdre's charms.  To make matters worse Barris became addicted
to a drug.  With all these things happening will Barris ever find 
the cure for Anikas' behavior?  Will they ever get back together 
even if he does?  What about Deirdre and the horrible things she 
does to him, will she get what she deserves?  Will Barris' son live?
How will this all turn out?  The only way to know is to read the book.