This one isnt an urban legend, it actually happened. I went to a catholic primary school, the principal was a nun, we had weekely hymn lessons with another nun, the school was built on the ground of the old convent, all that type of stuff. Mine was the last class to have the principal teach us before she retired and went to do nun stuff full time, she was a battleaxe of a woman, insisted on kids going to mass every week, got in trouble if you didnt, would treat the religious kids better than the rest. She even still had a cane she would smack on the desk since she wasnt allowed smack the kids with it anymore but every now and again your finger might get caught if you werent careful, she was a proper old school nun.
Went on to secondary school anyway, moved away from that area, generally got on with life until about 10 years later I was having a chat with my parents about the good old days and my mother informed me what became of her. A few years after she retired she met a man and fell in love with him so she left the nuns and eloped with him. This led to her telling me what happened to the original priest that was attached to the school, we got a new one about halfway through my time there even though the one we had was pretty young. Turns out the original fella had done the same thign as the old nun, met a woman, fell in love and left the priesthood. When you do the numbers it means 25% of the clergy attached to the school took lovers and eloped it in a 10 year period.