The following is a list of reasons why it may be difficult to date someone that you work with.
1. They are always there - Most likely you met this person at your job, which means you see them there. But, by dating them, you are also going to see them outside of work as well. This may sound nice in the beginning, but you both may get tired of this very quickly.
2. Less of A personal life - Once you start dating someone, you loose a bit of your personal life. This often takes a little adjusting to. Where you didn't have to worry about anyone but yourself before, now you have to take someone else's feelings in to consideration. When you work with the person, you ensure that you will get less time to yourself, and not only are they involved in what you do after work, they are also involved in your work life too.
3. Authority conflict - This is for couples who work close together and one has a higher position over the other. This can be a problem in to ways. The first one is that your partner may feel that they possess certain benefits above other employees. The other issue would be is if one partner actually receives benefits above other employees. It could cause resentment and conflict among the group.
4. Competitiveness - This applies to dating couples who posses the same position in a competitive field such as real-estate, or stock market where you are supposed to do your best to get more money. Without having a girl/boyfriend working with you, this can be a problem, but it is even more of an emotional issue when it is.
5. Legalities - Finally you have the issue of legalities. Many places don't allow employees to date each other. Almost everyplace forbids a boss and his employee. But further more, there is the chance that if you are in a position of power you may be used to get a person to where they want to go or visa-versa, where a person of power may abuse his authority to get something out of someone else.
On a happier note, dating a person at your job may not be all that bad. Sometimes it is nice to see a person at work especially if you work other jobs where your time is limited. Further more, there is a common ground that you can always talk about. There is less secrecy and jealousy as couples know that their partner is at work. If you can handle all of the above then you may find dating someone at work fun and exciting.