There are folks who have low esteem, or multiple realities (their real one and others that they use on The Internet, in church, etc.)
Some folks, more than you might think, have personality disorders: bipolar, borderline personality, low self esteem, anorexia, self-loathing, religious conflicts, and so on.
Sometimes folks have multiple identities on The Internet, or they steal someone's identity, or they're parrallelized by mental illness that keeps them living in fear.
Here on Real Jock, we've caught one guy who morphed his pictures, juices up, and lies about it all. We've exposed him, too, because folks like that are dangerous to others. It's really pretty disgusting.
If someone leads multiple lives the best advice is distance: between you, and them.
If someone can't be honest about something basic as their appearance, or as simple as sexuality, or if they won't be honest about their lifestyle, common sense says to LEAVE THEM ALONE. Run, Will Robinson, run. Life is to short to deal with crazies.
As a general rule, if someone is "quitting", "just out", or "discreet", they're flags for larger, underlying, disorders. RUN.