Long distance means that you have all the challenges of a normal relationship + the distance.
The fact that you can't check what your girlfriend or wife is doing means that you need to multiply your level of trust.
The way to solve unwanted jealousy is the same as if you were living together. You simply need to empower your "trust muscle" and reinforce extra qualities like respect and freedom.
With the internet communication tools like webcam chat and email, distance is no longer what it used to be.
Every now and then, have a deep conversation to see if your relationship is actually giving you both what you want.
If you notice a sign of disatisfaction, you need to take action and make sure that your relationship stays exciting even with the distance.
How to make and keep your relationship exciting is a whole different topic.
The first step though is how to tame a jealousy response when it appears and turn it into trust.
This is exactly what this e-book and MP3 audios teach you: