If you and your significant other (S.O.) are in a long-distance relationship, it's a sign that your lives are different enough that circumstances prevent you from living in same ZIP code, state or even country.
Maybe you just met but don't know each other well enough to move to the same city. While there's strong chemistry, both of your lives are chugging along on parallel tracks. You can't just sell your house, quit your job and move. Or can you? And what if you moved but it didn't work out? What if he or she moved to your city (or into your home)? Would it be a dream come true or a suffocating nightmare?
Or perhaps you started off together, but circumstances, dreams, desires or conscious decisions created the physical distance now between you. It's important for a relationship to foster a sense of togetherness, and that the bond has a mutually acceptable sense of stability and momentum. But over time in a long-distance relationship, you may feel as present in your S.O.'s life as you do in the life of the coffee-shop regular you keep bumping into in your own ZIP code -- and you may realize the same could hold true for your S.O.
If further long-term commitments are made by both parties (like a lease extension or acceptance of a big job promotion or transfer), and those commitments don't bring the two any closer together, someone's likely to pull the plug.
When the cat's away, the mice read the next page.