This time of year, the booze are flowing, colleagues are letting loose, and emotions are running higher than usual. Don't let any of that lead you down the wrong path.
For reasons that aren't at all obscure, a lot of office affairs start during the holiday season. With that in mind, here's some advice from somebody who's been there and done that:
1. You won't be fooling anybody.
You may think that you're keeping everything secret and that nobody can tell that something's going on. But you'd be thinking wrong. There is no office gossip more juicy (and more likely to spread) than "guess who's boinking?"
More importantly, millions years of evolution has optimized the human brain to sense pair-bonds because they're crucial to the survival of the species. Heck, most of your coworkers probably knew the two of you would "get together" before the two of you did.
2. Your reputations will take a hit.
If either of you is married or significantly-othered, everybody at work will adjust their opinion of both of you downwards. People will inevitably question your integrity and trustworthiness. A cheater is a cheater is a cheater.
If both of you are single and unattached, your reputations will still take a hit. People will start seeing each of you as part of a couple rather than individual contributors. They'll assume that you'll share anything told to you in confidence.
3. Your work will suffer.
There's no way the drama of the situation won't creep into your work. At best, you will both be distracted, and if the two of you must work closely together, whatever is going on in your bedroom will be reflected in the conference room.
If one of you is "favoring" the other (like giving your honey plum assignments), you'll be alienating everyone else, which will make both your jobs more difficult. Even if you're studiously ignoring each other, that's a strain that will distract you both.
4. The break-up will be awkward.
It's bad enough when any relationship ends, but it's worse when you're forced to work with your ex. Most of the time, the end of an office affair means one of you will need to find another job. At the very least, the break-up will further damage your ability to add value to your company.
5. You probably won't follow this advice.
If you're in love or lust, you're probably not going to listen to my advice. Despite all the hassles, the trouble, the lost work, lost hours, and lost dignity, you're probably still going have the affair and face the consequences. At least now you know what they'll be.