I really like this post, if i may add anything...About Erynn tho (ye I'm late, sue me)... I see a lot of people saying she has an "obsession" with MC or a stupid crush or whatever, but IMO you guys are forgetting one thing: It's not so much a crush as it is the fact that they were childhood best buddies (and neighbors).
Now, granted, there are some poorly written sections in the game, but overall it was clear to me that Erynn is a lonely chick who's had a lot of issues with men, and she sees the MC's return more as her best buddy coming back, hence why she struggles with romantic feelings towards him once she sees he became hot and all that.
So basically: MC is the one who has had a crush on her forever, Erynn did like him, but probably not at "crush" level, she is just happy that her childhood friend is back because she doesn't seem to have any male friends (and not many female friends for that matter) and has been struggling with a lot of shit. But things start getting complicated if the MC tries to romance her... You'll notice that she only behaves as BFF if you don't romance her, and she still wakes you up and comes into your room all the frickin time because she misses her BFF, not because she wants the D.
She does seem to desperately want to go back to a "simpler" time in her life when they were kids tho, she really acts in a very childish manner towards the MC, but that's very much in line with what I'm saying.
So in short, I don't think Erynn's badly written, or at least to the extent some of you claim, and I think her character makes enough sense... I'm not saying it's perfect or anything, but it's good enough that I got the gist of what's going on with her.
Erynn loved the young MC like a brother (hey incest fans!!!) and she wasn't aware she was making him horny(which is dumb, specially given things like she let him squeeze her boobs, but alas), and she was surprised when he wanted to be more than friends.
I think upon meeting the adult MC her psyche gets all out of shape, one part of her wants to go back to the same life she had when she was younger(and happier), and another part of her remembers his declaration and sees he's all grown up now...
Enter confliciting unresolved feelings, unreasonable jealousy and "hot/cold" behaviour.
I'm unable to retort to this, it's very well reasoned, and it makes perfect sense...It is, I agree but see it from MC's eyes. MC does hate Ethan. When he came back, he is unsure about being friends with Erynn again. Erynn is always secretive about her relationship status, i.e. she got furious when Mel said she was single. Then he sees the photos, she still has Ethan's photos in her place and saw Erynn went to prom with Ethan etc. When he asked about prom she just brush it off with using gaslighting 101. Then suddenly Ethan showed up at the door calling Erynn babe etc. At this point he is suspicious about Erynn dating Ethan, she again brush it off with calling it only business. Then Erynn ditches MC for going on a date with Ethan, MC caught them red-handed while handholding. At this point, he is sure Erynn and Ethan are dating. When he saw Ethan and Erynn fighting it's a couple fighting in a back alley. Why should he put himself in danger at this point? Erynn is no longer a friend to him, she kicked him out at his worst without an explanation and she is dating his mortal enemy. There was no reason for him to intervene.
We are aware some of these are not true and some others forced on her by Ethan but we only know these from others' POV, MC does not know any of these. It's not his business so he just walks away, nothing evil about it. It's not a dick move either, MC is not a superhero who helps damsel in distress. Even thinking she got what she deserves is not completely out of ordinary because she is dating Ethan.
Yet i still like Erynn, because at times it isn't about who is right or wrong it's about what story hits the right notes for you(and i'm a little drunk lol).