Something has shifted. The phone goes with him to the bathroom now, there's a new password, and a name that used to come up easily in conversation lately doesn't come up at all. You aren't being dramatic. Suspicion is rarely conjured out of nothing, and a pattern you've noticed is information, even when nobody around you wants to hear about it.
Information is different from a conclusion, though, and that's where the cards earn their place. A reading can describe the role a third person plays, the kind of pull she has and how much room she takes up in his attention. It can't give you her initials, convict anyone, or promise you how things end between him and her. A Seven of Swords says something is being kept out of view, and the cards around it tell you whether that secret is a woman, a debt or a job interview he hasn't mentioned.
This book teaches you to hold a reading about someone who isn't at the table. Part One shows how a third person tends to appear in a spread, through a court card that doesn't belong, crowded Threes and Fives, and Swords full of words not spoken. Part Two reads thirty-five cards for this one situation, from the Three of Cups and the four Queens to the cards of the one left out and the cards that bring you back to yourself.
In Part Three you lay the Triangle spread I use most, along with What Am I Sensing, Does He Choose and the Clarity spread, and you watch three readings worked through. Part Four takes the situations women bring me again and again: he's changed and I can't name why, he still talks to his ex, is it just friendship, he left me for her, he's married and says he'll leave. There's also a chapter, with no lecture in it, for the woman reading from the third corner.
When you finish, you'll have a way to separate what you've seen from what you fear, a plan for the nights when the doubt gets loud, and a steadier hold on the one corner of the triangle you can actually move, which is your own.