People

So I'm planning on moving out and taking the old ball and chain with me. Now I'm not planning on doing something stupid like renting, I'm doing it right and buying. Now every person I talk to at work says this is a bad idea. And everyone says that for the same reason. That after a couple years when it can be considered common law, she will leave me and be entitled to half my place. Am I being too naive or are people far too cynical in assuming that she would try and hose me for tens of thousands of dollers.