You are very wise to keep this relationship quiet. Keep doing that for now.

It's possible that this guy may be the best potential life partner that you will ever meet. If you see him as having that kind of potential, then I would give him a chance. But, if it becomes apparent that he is casual in his attitude toward you, then I would bolt. Working with someone you are dating is not all that big of a problem. However, working with someone you used to date can become a nightmare. I hope he is a discreet sort of person. Listen to how he talks about former girlfriends. That may give you an idea as to how he might someday talk about you. Don't rush into sex, if you haven't done that yet. Don't share all your deepest secrets yet.