Breaking up
Do not expect being able to keep it secret, soon everyone knows for it is a juicy item for the grapevine. However, don’t make an announcement about what happened. Change the subject whether and when co-workers notice the change themselves and ask questions. Deny your ex any requests to "talk" on the job about anything that isn't work-related. If you must hear your ex out (for example, he is your boss) then let him know it's only going to take place outside of work. Move your workstation or apply for transfer to another annex or country. Rethink workplace romances in the future.