There are some good answers here from the company point of view, but look at it from the human point of view, too:
1) Do you really know the other person is interested in you, or is it just a shared interest in the type of work that you do? I know I leave a great deal of my personal interests in the parking lot when I arrive to work. I focus on my work and ensuring that I am supporting my coworkers and meeting my objectives. I don't bring much else. Since you are a business owner, I imagine you are much the same. Your employee may also be the same, meaning everything you see about them "lines up" with you, but you are both (likely) leaving a huge amount of who you are outside the workplace unexamined. How do you even know you would be compatible?
2) You have authority over the other person at work. How could you ever have a relationship of equals when you have power over their means to make a living? The power dynamic in a relationship can get really messed up if there is a disparity in income between the two. You are the income source for the other person. How could you ever hope to have an equal, balanced relationship?
3) What happens if they get a good job offer from a competitor? You would feel personally betrayed if they took it. They would be resentful if they didn't take it because of this relationship.
4) Their relationships with their coworkers at the office would be devastated. No one would ever have a "gripe session" about the company with them. No one would trust them with any confidence, believing (and rightfully so) they were more loyal to you than anyone else. I'm sure you're the world's greatest boss, but running a business means making your employees unhappy in order to satisfy your customers. That's why you have to pay employees in the first place. Would you avoid giving them difficult assignments or "problem" customers in order to safeguard your relationship. Maybe not consciously, but it would happen.
5) You would never evaluate them equally, again. "Bob" is always late, so you discipline him. Your interest is always late, but you cut them some slack because you took them out the evening before and you feel it's partially your fault. Bob isn't getting a fair shake.
Look at it from the relationship side, and not just the company side.
Now, the only way to fix this is to not work at the same company. Who has to leave and who gets to stay? Who gets to pick? In your case, you and the company are the same thing, but not so in most situations.
Say I'm a rock-star senior salesman, been in the biz 20 years and have 5 or 6 million in annual sales that I bring in. You're an inside sales rep who answers to me supporting my customers. We get serious, and it becomes a problem in the workplace. You would have a hard time finding another job in a slow economy, but I can hop over to "Brand X" and bring at least 2 million in sales with me. Brand X says, "Great. Welcome aboard." The first company now just lost a good salesman, $2 million in business, and has an inside sales rep with questionable loyalties that "cost" them all of the above. How do you think your chances of promotion are, now?
That's why intra-office dating is never a good idea. Working with a spouse is another potential disaster, but for entirely different reasons.