I am the hinge of a V, and am and have been in long-distance relationships.
I'm from Europe, my husband is Canadian. We first dated online, for about a year, meeting each other once in the middle. Then I spent a year in Canada. Later, he went to Europe and we lived there together and got married. And after two years we moved to Canada together.
There are lots of challenges to LDRs. The main problem for me is a bit hard to explain, but let me give it a try:
When you're with someone face to face, you don't have to be productive. You can be just sitting there. You can be each doing your own thing. You can be walking silently.
When you're "together" in a long distance relationship, and by that I mean when you're separated, but talking online for instance, you have very limited options.
Nothing physical is possible of course. No snuggling each other or just being next to each other. But you can't easily be doing nothing while still being together.
So when you're talking online, but feeling like just relaxing, it gets frustrating at times. It's like you have set your time free but you're not doing anything with it, not getting anything out of it. You can't read a book and still "be together". You can try to feel this way but it takes a whole lot of work. Usually, you're either talking or separate.
And there is only so much talking you can do before you wish you could grab something to drink, take a walk and just lie there next to each other in bed and look at the ceiling.
Or, of course, have sex.
Then, when you do meet each other, it's so rare, and you know you have to make the most of it, so there can be some pressure. "We HAVE to do X or Y. Everything HAS to be perfect".
It takes work to let it go and just enjoy the present.
Right now I have a long distance relationship with my boyfriend, who lives in the US. If you have any question I'll be glad to answer it.