Can I be fired when my boyfriend gets hired at the same place?

I have a job in a factory working midnights. I have been there 6 months and it is a union so unless I really screw up, I will have a secure job. My boyfriend is a university student, like me, so our time during the day to work is nonexistent. He is going to be hired in a month at the same factory, same shift, as I currently work. We have worked as custodians as a team last summer with no complaints/problems and our bosses knew we were dating. My question is, should my boyfriend and I tell our superiors we are dating or is that an issue that is private and as long as we maintain a professional relationship at work, not an issue people should know. I can't afford to get fired and he really needs this job. Any advice would be great. I live in Ontario, Canada (in case the laws vary from place to place).

I have tried online research to no avail. My superiors are not very helpful with human relation issues and there is no section about dating in the contract. There are brother working together and an aunt and her niece but no couples. So they have nothing against family working together.