Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of crush],
I know that you have noticed lately awkwardness between us, and that I've been distant. I hope you don't think that I am mad at you, or that I no longer want to be friends.
The truth is that I have begun to develop feelings for you. I know that dating among coworkers is generally not a good idea, so I've attempted to distance myself from you. However, I have found myself more and more drawn to you and not speaking with you or hanging around with you has done nothing to change these feelings.
I am telling you about these feelings in the hope that you are interested as well.