Virtually every victim (invariably women) of narcissistic abuse that I have counseled found out that their lover had one, two, and often three secret lives. Usually men, typically sexually involved with several women at a time, none of whom know anything about the others' existence. The sociopath carefully structures these separate worlds, crafting the web of lies, immune to the risks and guilt that others would normally feel. (Note: this is so common that the Investigation Discovery Channel actually just began airing a show called "Web of Lies").

The abusive narcissist smoothly compartmentalizes these lives, creating different False Selves who act differently with each lover and within each life. In fact, for the sociopath, lying is a way of life much like religion is for others.

Think about famous examples of double lives (all abusive narcissists/sociopaths): Tiger Woods, Josh Duggar, Sandra Bullock's Jesse James, 7th Heaven dad Stephen Collins, Bill Cosby, Bernie Madoff (cheating his friends out of their money), Gary Ridgeway (The Green River Killer), Ted Bundy (he was married when he was killing), TV evangelist Jim Bakker, Arnold Schwarzenegger, John F. Kennedy, Anthony Weiner....I could go on and on.

Here are the signs that your partner is leading a double life:

His time away from you is unaccounted for or he makes it strangely confusing. Traveling for work, working late, overtime, running errands, last minute obligations all can combine to paint a picture of someone whose splitting his time between two worlds. One serial rapist and serial killer told his wife he'd leave in the middle of the night to "take photographs around the city." Who DOES that? If it sounds weird, it is.
He bans you from the garage, basement, his desk, or his computer. He may not want you to discover the proof of his double life evidenced by emails, credit card statements, cell phone bills, or hidden objects.
He lies. This is obvious, but you would be surprised how many people forgive liars. One lie is too many. More than one is pathological. Listen to your gut.
His sexual patterns are confusing. He may suddenly become impotent or have a voracious appetite for porn. Or he may be impotent with you yet masturbate to violent porn. Degrading or violent sex is often an indication that something frightening lies beneath.
He keeps secrets. There are few good uses for a disposable cell phone particularly when that person already has a legitimate cell phone account. Same thing goes for secret credit cards. Why have these things? He may have a secret family!
Your family and friends don't like him. Take him home at the beginning of your relationship and see what your friends and family say. While you are in the Idealization stage, their sociopath detectors will be working better than yours.
You find strange items. Women's panties between the couch cushions (this one really happened!) that are explained away with a lame excuse. A disposable cellphone or unknown numbers appearing repeatedly on a bill. A disguise (also really happened). An inordinate or inexplicable amount of money. All bluffed through as misunderstandings or completely being reasonable. The sociopath will explain the most bizarre things as being completely normal, and then turn it around on you to make you feel ashamed for questioning it.
Incongruity. You notice strange objects. Odd smells, He becomes angry for no apparent reason. John Wayne Gacy's wife lived in their house for years with the smell of rotting corpses beneath her, which was explained away by her husband as dead mice.
Detail confusion. Can't remember your birthday or whether you went to Maui? He's confusing you with someone else.
Criminal activity. Seemingly petty crime can be a big red flag. Theft by deception is another word for a con. White collar crimes like fraud or financial crimes, and fights or assault are common. Multiple DUI's and anything beyond are signals to walk away.
If it seems odd, it probably is.

Listen to your gut. If you think it is strange, it probably is. Time pay attention and take action.