I've thought about this from the perspective of anxious attachment & avoidant attachment. Obviously these dynamics show up most in romantic relationships, but as someone who skews anxious, I'm aware of how this stuff shows up in friendship, too.

I have an avoidant friend who is pretty bad about keeping in touch. I've learned to allocate my time for her around enjoying her time when she's made herself available, and lovingly putting her out of mind when she's not. It's not my job to check in on her, when that level of attention is not reciprocal.

It's an ongoing practice of nonattachment and compassion. I love her for what she brings when she's able to show up... and release attachment to it being anything other than what it is.