Relationship maintenance can be difficult. Somehow, I never know what the right amount of "checking in on each other" is. Am I supposed to text every day? Call once a week? Once a month? It is hard to tell for me and somehow I never developed a "natural" urge to check in regularly on the people I know and care about.
At the same time, I think that some people have very specific needs and expectations around these issues. There is the keeping track of who called them for their birthdays, the "you never talk to me first anymore, the "you are not calling often enough". It's hard to know what to make of it.
On the other hand, I have been in situations where I have made a conscious effort to reach out to people a couple of times only for them to not reply or be busy. I get how that makes it hard to figure out whether someone truly wants to spend time with you or not. I had this one friend who never contacted me first but she'd always seem super happy when we met. I still doubted if she wanted to be friends. It is hard to distinguish between "just busy with life" and "I don't really like you".
these days, I try to talk about these things head-on with the people in my life. I ask what their expectations are and what they think their communicative patterns are. They differ a lot from person to person. Some want regular contact and some just want a nice chat once a year.
I learned that how much you care about someone is not necessarily proportional to how much you talk to them. Sometimes it can even be the opposite.
I also learned that it does not always matter what the other person thinks. If it bothers me that I have not talked to X in a while because I really like talking to X, then I should just talk to X more. Sometimes that means putting a reminder into my calendar, other times a spur of the moment call-in is enough.
When I think things are getting a bit one-sided or a person is too busy with their lives (like my dad, for example) I just tell them "Look, I have been reaching out to you a lot but somehow you seem busy right now. That's totally cool. I want you to know that I am not angry at you and that I will always pick up the phone when you call. Other than that, though, I will probably reach out to you less." This works especially well in cases where the perceived rejection hurts me (again, as is the case with my dad).
I like saying this: You are always welcome in my life. I'll always pick up the phone. Come whenever you feel like it.