I feel that the Alexis/Erynn relationship is established well. They have been together since early childhood (the first flashback). They have been together for years (the annual tree picture). And numerous comments amongst the MC, Erynn, and Alexis show Erynn and Alexis are very close. The fact that we do not see them together so far is because Alexis has been romancing the MC despite knowing how Erynn feels about him. Out of guilt and shame, she avoids Erynn until it all comes to a head.
I also feel positive about Erynn and Alexis. So I know that plays into how a player views each character. Generally, if a player does not like Erynn, they will comment on her lack of scenes or her lack of claim to the MC. For Alexis, the fact that she is hiding her relationship with the MC from Erynn, that she has lied to both of them, is the reason most discussed.
But, we know that Alexis takes her fight with Erynn very personally (and vice versa). We know Alexis drops everything to search for Erynn at the end of Ep. 9. And we see the MC working to bring the two back together. He comments on how important they are to each other. This is a matter of speculation, but I think will soon see that they need each other and how Alexis helps Erynn out of the upcoming situation.
I think it is the result of how chapters are released and us viewing a preview of a work-in-progress. If we were to get a chapter-by-chapter preview of a Stephen King release, we would be asking a ton of questions and frustrated that we are only seeing a piece of the puzzle at each release. Any movie released the same way, any series we watch with cliffhanger endings to each episode. We give the series/show/book a bit of trust and faith that the story will be told in time. This visual novel is no different.