Criminal activity in the past or present, infidelity, pathological lying or involvement in espionage are powerful motivations for someone to lead a double life. Many people go to great lengths to conceal the truth. If you suspect that you are being deceived, tread carefully; mistrust can irreparably damage relationships.
Extract as many hard facts about his previous life as possible, including birthplace, family, education and previous jobs. Do not rouse suspicion by seeming overly curious. Try to sound interested and conversational by asking open-ended questions that encourage him to give long answers, rather than questions that can be answered with a simple yes or a no. Freely give information on your own life.
If you suspect you are being given a false name, look at her credit card, driver's license or passport. Try tricks like showing her your ID photo, laughing at your bad hair or dumb expression, and asking to see her photo; or admiring her wallet and asking to take a closer look. Most people carry information that reveals their identity.
Search online using his name and keywords such as previous jobs, schools or his stated hometown. Gather as much information as possible. Look for details that do not match what he has told you about his life. This will only work if he has told you his real name. If he has access to your computer, delete your search history and cookies afterward.
If minor details are different from what he told you, is it possible that you misunderstood him? Next time you meet, double-check the facts as casually as possible, either by pretending you have forgotten the details, or by asking an unrelated question that will confirm previous information -- for instance, "Did you play any sport when you were in college?" or "Did you get to travel when you worked in Hungary?" If he confirms a story you believe is false you know something is wrong -- and if he changes the subject or becomes defensive, the chances he is lying are high.
If you have uncovered anything to arouse suspicion, consider involving someone else in your search. Do not take this step lightly; once you have brought your search into the real world -- for instance by hiring a private investigator -- you cannot go back. You are increasing the chances of being caught, and if she is not lying you may damage an otherwise fulfilling relationship. If you decide to take the risk, contact companies or alumni societies at the schools she claims to have attended. If you suspect illegal behavior, see if you can get a criminal check by using your state government's criminal website page -- some states charge for this and others do not. If you need professional help, hire a private detective.
If you discover major inconsistencies between what he is saying about himself, and you want to know the truth, confront him. Choose a public place, because if he is lying for legal reasons you may be in danger. Also, pathological liars can be aggressive when exposed. Remain calm and reasonable and watch his reaction carefully. Prepare for shouting, aggression, tears or guilt-tripping. If he denies guilt, watch for tell-tale signs of lying, such as avoiding eye-contact, crossed arms or legs, sweating, tripping over words, or speaking in a high-pitched voice, according to learnbodylanguage.org. Remember: these are not fool-proof markers because they are also signs of stress. You are accusing him of lying, so he is likely to be stressed.