Just out of curiosity.
I suppose it depends on your age. A long-term high school relationship is a year. In the adult world, it’s not long-term. I would say 3 years or more is long-term in your 20s. Add a year to that with each decade, I suppose.
Perhaps it would be better expressed as a fraction of the age of the participants?
I’d say if you’ve spent more than, say, a tenth of your life so far in a relationship, then it’s long-term. Actually, maybe that needs a bit of fine-tuning. A twelfth, maybe.
~ Isaac
I say it’s more complicated than that. You can’t say, “X amount of time is long term,” or even “f(x) amount of time is long term,” where f(x) is a function of age. No, whether a relationship is long term depends on what the participants want out of the relationship. Case in point: my own relationship. My girlfriend and I have been together for almost a year and a half, but we both seriously intend to pursue the relationship and the probability that we will be getting married someday is significant. In other words, long-term refers not to how long the relationship has lasted to date, but rather to how much longer it will last.
For myself, and taking into consideration that I had every intention to remain single, the past fifteen years with my husband, with every intention to remain together (we had a talk about this not too long ago) this qualifies as long term.
I agree. It’s a long-term relationship when the people in it are in it for the long-term. It’s subjective and subject to error, of course.
Agreed, however, a “long term relationship” that’s only been going for a week, wouldn’t qualify IMO. It’s more of a “state of mind” thing than a “time” thing.
I was planning to move in with my (now) wife after 6months of “togetherness”. It was certainly long term by then.
5.5 years and a beautiful daughter later, it had better be “long term”! 
DOH :smack: , in case she reads this… 5.5years of blissful marriage, and 7.5 years of wonderful togetherness.