I see what you mean. Still, I have had that happen to me once. It was just for 2 years, but I was still pretty surprised when she came home from visiting her adventist church, telling me she will move out. When I asked about the whys, she suddenly had a complete list of things which she couldn't stand anymore. However, she never tried to talk about any of them prior to this event. In fact, I even asked her a few months about one of the topic on her list, and she told me straight out it was fine with her. To be honest, I really should have sticked to my rule of not dating religious women. I still suspect her church mates had something to do with the sudden change in attitude. However, I never learnt what was really going on. Go figure.

The upside of such events, which has been mentioned by others already, is that you are now free to find the right person for you. Breakups, while sometimes being pretty emotional, are almost always for the better.