Lying and the long-term consequences

The regret-filled woman Susan mentioned isn't the only one to come to regret lying about her sexual history:

An unfaithful wife has been jailed for two years - almost a decade after she cried rape just to hide a one-night stand from her husband.  Gaynor Cooke, 41, had told police she was violently attacked by a taxi driver to cover up her fling with him, and her former lover was due to stand trial next month.

No-one was arrested in 2003 because a forensic sample taken from her at the time failed to find a similar profile on the national DNA database.

But when in 2011 the man, who she claimed was a stranger, was detained for a minor offence his DNA threw up a match.

The truth doesn't always come out, but it comes out often enough that it simply isn't worth the risk.  And it often comes out in unexpected, totally unpredictable ways that aren't usually at a particularly convenient time.  If you did it, just own up to it.  It's not just the right thing to do, it's the safe and responsible thing to do.