It's hard! I have a friend who sometimes never responds to texts or takes months. Other times, she responds much quicker. I used to cry about it feeling so lonely and like I cared about the relationship more than her. I guess I just kind of got used to it after awhile? She's much better in person. Some people aren't very good about responding to texts, etc. Different personalities, love languages. And some people aren't good friends/family members.
Could be the person's problem and you might not have that issue with others. If you're taking it as a reflection on yourself - even though it's difficult, try not take it as something personal. The only thing we really have control over is ourselves. Sometimes guided meditations focusing on acceptance have helped me when I've wished a relationship was better than it is.
I hope this helps and doesn't come across as preachy.