as i get older, i come to accept that people do come and go, even when i have a reasonably good relationship with them. and there is nothing wrong with that.
try to see the life we live as a long story book, and the people we encounter as characters in that story book. some characters have roles in several chapters, some characters show up as mere mention in one or two paragraphs, and some characters last through the better part of the story book. one crucial point: regardless how short or long their presence is, or how good or bad their characters are, they ALL are part of the story. they are what make the story distinctively ours.
inevitably, some characters’ time is up. they are no longer part of the next chapter, or they are not that relevant anymore. and that is normal. we ought to learn to cherish them as part of our life story. and let them go as necessary.