When my SO and I met, I was living in the north of Europe, he while not French was living in France. So, we were separated by 1500km, or roughly 2h of flying. Now, this may not be long, but consider these additional constraints:

• it was 2h by SK, which means typically expensive;
• we were both in the last year of our studies at the time, thus not much cash available for traveling (nor time, for that matter).

We'd see each other about once/month (me taking an evening job on a gas station to fund that) in our respective countries.

Now, there's something very good about this: whenever we saw each other, it was on a sort of "vacation" where we put everything else to the side to be together. The downside was exactly the same: that we didn't get to have a "day to day life" with each other during that first time where we were both forgiving due to being madly in fresh love , but that we only saw each other in "vacation-mode" of sorts.

In other words, and as a previous poster has mentioned, each of our respective "weird habits" in the day-to-day-routine didn't get the benefit of a "cushion" of being freshly-in-love to allow ourselves to adopt to each other....

Anyways, studies had to end some time, and so after a bit more than a year we decided to try it out together -- and off I went to Paris...

...and now more than 10 years later, we're still happy together

The secret? I think that one of the things that helped was, that we discussed this beforehand: that it is going to be difficult since we never had a real continued "dating-period" before moving in together, and so we should "talk to each other rather than become irritated" over the small things. Also, we both knew that moving country was a "big deal" in and by itself (financially, socially) and so we were determined to make it work.

Ohh, and most importantly, of course, that we were and still are in love