Dear  Ava:

be gentle with him as you give him the clear message that you are not interested in a romantic or physical relationship with him, that you are only interested in a friendly co-worker/ professional relationship with him. Make it short, clear and no double messages. Better not elaborate and say too much, the more you say, the more chances there are for misunderstanding on his part and false hope.

After you communicate with him this way that one time, be consistent afterwards- do not see him outside of work, do not flirt with him or suggest anything at all that may give him false hope.

anita