Is it wrong for me to accept the very real possibility (in light of social trends in the past decades) that my current partner and I might well break up, for reasons yet unforseeable, in the future? It seems a rational judgement - a large number of marriages don't last, and unmarried partnerships even more so - yet I can imagine that I would be upset if my partner accepted this possibility as one of those "facts of life" we have to deal with.
It is certainly wise to take these statistics seriously and to realize that you and your relationship are not immune from those trends. Yet, I don't think the ideal response is to 'accept the possibility' that your relationship will fail, but instead you should ask yourself why relationships fail so frequently in our society and take steps to avoid those pitfalls. If you do all the same things that everyone else does, you should expect the same results. If you take extra steps to protect honesty, intimacy, closeness, commitment, fidelity, etc. in your relationship that other people don't take, you are more likely to succeed.