Depends on how reliable that due date was. Not, how close to it did the baby actually come, but, when did you get the due date in the first place, and how? Was it in the first seven weeks of pregnancy, by an ultrasound? If so, your chances are OK (not a thousand percent slam dunk) that it is your boyfriend's baby. But if you got the due date later in pregnancy than about the seventh week, and/or if it was counted by the doctor on a calendar or a little cardboard wheel from your last period, it's a total tossup. All you can do then is hope the brief exposure with your coworker was not productive.