Easy to say, hard to do. We don't like change. Change means possible danger, it means relinquishing opportunities, it means no safety net.

Part of the happiness that comes from a new relationship comes from not just discovering new things about each other (or NRE, or the Coolidge effect) but from the (misplaced) belief that things will go on this way forever. Embracing change means sacrificing that pleasure, which you might be able to do if you possess foresight/discipline, but it is hard and not obvious, especially when you have an of love that's foolish, us-against-the-world that reinforces that mentality.