There are certain scenes that would take place "behind the scenes" that we don't get to see. Every interaction between characters is not possible. Conventions we make as we are reading, assumptions. If they are best friends, then we must assume that Alexis does visit her, call her, text, etc. we are simply not privy to those interactions.
If the MC is not pursuing Alexis, why doesn't Alexis look for her at the end of Ep. 9? My best answer would be so that we can see some of the other characters in action — John or Valeria. I do not think it was an oversight or an attempt to illustrate a problem between Erynn and Alexis. After all, if you were playing an Erynn route only, you would not "know" anything about the relationship between Alexis and Erynn other than they are best friends.
There are limits imposed by amounts of coding, rendering, storytelling, releasing frequency, etc. that restrict how much content can realistically be added. The story is not about Erynn and Alexis. Why would the author focus so much attention on that relationship outside of how it involves the MC?