See all friendships continue as long as you have something in common. Childhood friendship is special because though you move out, whenever you meet it is like there has been no gap between you.
But in a nutshell close contact happens till you have something in common. We were a close knit gang of four during plus two days. Once degree happened 3 of us took electrical, 2 in same college, 1 in another, 4th one civil engineering. 1st yr we tried to be same as syllabus was same. From second near new friends were added and yes we met. But then you planned the meeting as each had their priorities.
Then job all four in four directions. Of course marriage, responsibilities, even less phone talk. But yes whatsapp group, hi forward etc etc happens. Meanwhile professional field you make contacts. Some friends whom you prefer to keep in touch. Rest after u leave the company some in FB that's it.
Even look at the forum. Have been interacting with you all for past say 5-6 months for sure. We had something common to discuss. SKR forum also I had some friends. Chat group is there. I do go there occasionally. We discuss. If we create a chat group also it will be very active for say 5-6 months. Then everyone will have their priorities, but you will come and check. That's how life is. Also even if you are close friends you might not hang out at times with your best friend as your tastes differ. So you will have a group for each of your activity. Its like how you manage change.