I deal with this somewhat as well. I have several people that I have good relationships with and we can sometimes go days without talking. I'm able to be OK with that. I also have one person in particular that I want to have a better relationship with. When we talk life is good for me, when I don't see or talk to them for days I'm always thinking the worst and am sure that they're with other people plotting my demise.

It seems to be the one I have the more fragile relationship with that I worry about and those that I have better relationships with I worry less about. Not sure if that goes into how things are working.

What I'm trying to do is understand that friendships or any relationships have varying levels of connectedness. We get conditioned by society and self-help to focus on what's wrong rather than what's right. So I worry about the one relationship that isn't good rather than spending more time with the people who I have good relationships with. And everyone has periods where they're busy or where they're dealing with things and I have to be OK with that. 99.999% of the time its just not about me.

My only advice is to reach out when you're feeling disconnected. Don't wait for them. But if you don't hear back right away, accept that they might simply be busy and then do things for yourself.