if you can't see each other often so they just start communicating less and less.
This is honestly not my experience.
Although I've moved around a lot, I am still in touch with some friends from schooldays. The key thing is not how often we are in touch, but the quality of that relationship when we are in touch.
Some love quite close, others live on a different continent. We don't get to see each other all that often, but when we are in touch or when we do get together, we fall right back into the closeness of forty years ago.
Frequency of contact is for me absolutely no measure of friendship.
I do absolutely know how tough it can be when you move away. My best advice for you is to really make an effort to find new contacts in your new area.
Be flexible and patient with new people. Ideally, you already have something, such as an interest in common. Don't dismiss anyone out of hand. Have a go at being a friend to them and see what happens. Many will slip away for all sorts of reasons. If you are lucky and persevere, some will stick.
You can still friends with the people you met before you moved. Friendships can expand almost infinitely to include other people, as the opening line of a poem by Chalker goes
People come into your life for a reason, a season, or a lifetime.”
All the best.