This is a situation one is most likely to face sometime. The body's natural urge for s*x, the fact that people can't avoid working in environments with people of the opposite s*x, friction occurs, sparks fly, a fire may result. If love is not all about s*x then why should someone divorce another for having it with another. If it's an affair then perhaps... But even so for all you know (or don't) you may have driven him/her right into another's arms. NEVER make a rush decision. Sit down and talk and see what's best for both. One stupid mistake, or judgement should not ruin what you've taken months or even years to build.