What are among your biggest fears about your primary relationships?

Think about your marriage or your significant other or someone else you are very close to. What kinds of fears keep you up at night, or make you think about them occasionally? How likely is it that each of these fears will come true? I.e., do you worry about things that are unlikely, or things that are likely? Or is it just a big fear, but you don’t worry much because it probably won’t happen?

What are some fears that may not be so big but that might happen? More realistic ones? Do you spend much time worrying about them? Or is this all pretty academic?