Okay somebody needs to help me out with this.

Up until Book 2 Chapter 6 of "Lord of Souls" Colin is gallivanting about with his partner/lover Arese.

Then...all of a sudden, as of the next time we read about Colin in Book 2 Chapter 11 he is being caressed by someone named Letine who seems to have exactly the same motives and description as Arese?

THEN, in Book 3 Chapter 6 she goes BACK to Arese! WTF?

What am I missing here? Who is Letine and where did Arese go? Is this a first and last name that isn't explained?

Arese, Letine. Letine Arese. First and Last name. Derp. I get brain farts too man. Happens to the best of us.

Letine Arese is the assistant to Minister Hierem, responsible for concealing Attrebus' intentions from the minister and Emperor. She appears to be a sorcerer capable of changing shape into a ferocious beast.

http://www.uesp.net/wiki/Books:Letine_Arese#Letine_Arese

That's what I figured but it seems a really poor writing execution to keep bouncing around between the two names. It is the only character that Mr. Keyes does that with and it seems to make no sense and have no logic to it, except perhaps, to display her double-edged nature? But even then it just comes across as indecisive.

I guess this was explained in the first book which I haven't revisited since it first came out.

Keyes DOES have an odd and fairly inconsistent writing style I must say. It is no wonder you got confused. I bet many people felt the same. I remember doing a few double takes when reading the parts about that character.