You are correct (if he does not tell you how he feels, you won't know)
If you are not interested in him, it is best to leave work and pleasure separately. Otherwise, you may find yourself in a potentially undesirable situation if he causes some problems for you at work. Also, employers have access to their subordinates emails and you may want to avoid using those for email exchanges with him.
You can still let him know that you're open if he'd like to talk to you. It seems that this is been going on for quite some time now especially if you never got together. Sometimes it is best to leave things as they are. This guy may be confused or not wanting to get in the open. Just ask yourself- how long would you want to drag this with him and what would you get in the end? If it seems more of a hassle, look elsewhere.