Being in one and happy, I can give this advice . . .
On the practical end:
1. Email regularly (approximately daily)
2. Set a “date” about once or twice a week
to talk with each other for an extended period
of time on Skype [in case you don’t know, it’s
a free video phone service you use over the internet;
download at http://www.skype.com]
3. Schedule vacations when you can see each other
in person. Depending on the distance, it could
mean “only once every few months or so”.
For this to work:
Both people have to have strong enough feelings
that they are willing to work through the
difficulty of being apart and strong enough feelings
to remain faithful to their partner (rather than
just swapping them for someone local).
During the period apart, each person needs to learn
how to communicate well with the other partner . . .
for one, to avoid misunderstandings; but also
to be able to talk about difficult issues from a
place of love and support . . . to build a sense
of deep trust from knowing that the other person
really cares about you, wants you to be happy,
and accepts you for who you are.
If both people can continue to develop the feeling
between them that each loves the other unconditionally
and that they really care for them, then feelings
of deep love will continue to grow and develop.