Livre d'Or

Sure it's legal - it says in my contract that I can be dismissed for not upholding the school's values. Also possibly without cause — schools like to reserve the right to make messy situations go away without having a battle. It was useful a couple years ago when a colleague got dismissed for inappropriate behavior towards a student.

And people who have relationships that aren't formalized in marriage aren't exactly a protected minority in the US. Is it different in the UK?

My school is kind — I might not lose my job. But the narrative of having a kid out of wedlock while teaching at a Catholic school... is not a narrative I want to have to deal with, any more than the school would want to have to deal with it. It would be incredibly socially awkward.