I think that a long-distance relationship doesn't work. Ultimately, I suspect that any relationship which is long-distance will either change into a short-distance relationship, or it will fail.

For a romantic relationship between two human peoples, they need to not only communicate, but they also need physical closeness. Long-distance can work as a temporary situation, if one person is far awar for a few months, but I don't think that an entire relationship can continue is it is long-distance.

My point of view that there is no "relationship" on the distnace for a long time. When a couple is separated for any reason (studying, workign or just even an internet-affair) it is hardly possible to have many things in common. I mean you loose the simple momemts of live like going to cafes, cinemas, walking, chatting and sharing important things. Moreover, not to mentinon the importance of physical touches which lead you to a real closeness. As a result, when you see each other next time (for instance, in a half of year or even once a year) you feel like a stranger to that person. 

However, some short-time distance could help you to check out the feelings to your partner and to appreciate him/her more :)

I think it's difficult but it's feasible. The distance is sometimes necessary.

it's beautiful but also unstable~

it's too painful, I'm not sure I could stand it.