If there is any important truths you haven't communicate to your primary partner, you forfeit the right to expect a good relationship with him or her until that truth is told. Most people don't realize this, so when things aren't going well in the relationship, they think the other person is the basis of what's wrong, instead of looking for withheld truths on their own part.
People often ask: "How can I tell if my partner is lying?" Usually the response is, "Don't worry about your partner -- put your attention on whether you're hiding any lies!"
There is, however, an unfailing way to find out if your partner is lying, and I will describe it for you as best I can. Understand, though, that the following methods, while quite reliable, can never be regarded as a precise science. Like everything involving complex human behavior, there is considerable individual difference.
First, make sure you really want to know the truth. These methods work very quickly, so before using them you need to be sure you choose honesty over delusion. Some people prefer the state of "blissful ignorance," while others prefer to know the truth even if it makes them uncomfortable. I absolutely recommend the latter as a path to healthy, conscious living.
Think carefully about the exact question you want answered. Sex and money are the two subjects partners lie about most. In order to get at the truth, your question, regardless of the subject, needs to be detailed. For example, don't ask, "Do you find Bill attractive?" if what you really want to know is, "Have you had sex with Bill?"
Learn the Three Red Flags that signal cover up. Here's what to look for.
No. 1: Body Language Indicating Concealment. In the first few seconds after you ask your question, notice if your partner shows any of the following body language:
Face-touching -- When you ask the question, does he or she suddenly touch the face or cover part of it? (Think back to Bill Clinton saying he didn't have sex with Monica Lewinsky, he reached up and touched his nose immediately after saying it.)
Arm/leg shift -- Does the person suddenly change the position of his or her arms or legs? Two common reactions: crossing arms over chest quickly and crossing one leg over another.
Eye shift -- When you ask the question, does he or she shift eyes away from contact or lock into a hard stare of excessively intense eye contact?
Body turn -- Does the person turn his or her body away from you slightly?
No. 2: Voice Mannerisms Indicating Concealment. When you ask a question that exposes a lie, your partner's voice will often give clues to the real truth. Listen for these reactions in the first few seconds after you ask the question:
Pitch shift -- Does the person's voice suddenly go up or down in pitch?
Speed shift -- Does he or she suddenly begin speaking faster?
Hems and haws -- Does the person cough, clear the throat or fumble around vocally with a sudden increase in filler words such as "er," "um," and "uh"?
No. 3: Attitude Reactions Indicating Concealment. Instead of answering a question with the simple truth, your partner may defensively avoid the question with a sudden display of attitude. Watch for these reactions in the first few seconds after asking a question:
Hostility -- Does he or she react with hostility? (For example, you ask, "Have you had sex with Bill?" and your partner responds with, "Why the hell would you ask a thing like that?" instead of a simple yes or no.)
Indignation -- Does he or she react with indignation? (You ask, "Have you had sex with Bill?" Your partner responds with, "I'm offended that you could even think such a thought!")
Turnaround -- Does he or she respond to your question with a question instead of an answer? (You ask, "Have you got any bank accounts I don't know about?" Your mate responds with, "Why are you asking something like that right now?")
Before asking the big question, first get a baseline by noticing if your partner shows any Red Flags when you ask innocent questions. Ask a simple yes-or-no question your partner is not likely to lie about: "Do you want eggs this morning?" or "Do you know when the soccer game is this week?" Watch the reaction carefully. You probably won't see any Red Flags in response to an innocuous question, but you need to get a baseline to find out if your mate does any of the Red Flags under normal, non-lying circumstances.
Pop the key question and watch the reactions. Be mindful of timing, though. Don't do any of this while either of you are driving or operating equipment of any kind. If you have children, make sure you ask the question when they're not likely to be influenced by any heated words that might ensue.
In my experience, the lie itself is just the tip of the iceberg. The real issues that need to be confronted are those that gave rise to the lie. Lies can be a force for destruction or a springboard to positive breakthroughs, depending on how you handle the aftermath.