I think Erynn makes an okay friend, if a little naïve and seems to have a really hard time telling people no. I also think she makes a terrible girlfriend for the same reasons. She falls for Ethan's shit time and time again and once she's finally realizes he's a classic douche, he's got something on her and is trapped. Of course, being the intelligent, mature person she is, she's gonna deal with it herself, and not involve anyone around her, like Melissa. Melissa knows what kind of damage a sex tape could do to Erynn, no matter the field she was trying to go into.
Alexis checking on MC after the confession was sweeter than almost anything Erynn has done story wise. Erynn showing up later to check on MC after he starts avoiding her (how much time passed?) is just her being too little, too late. Of course, we know from the letters she wrote that she did make a considerable effort to try to patch things up. It still doesn't scream romance to me at all, it's just a friend missing her other friend.
The only time I see what I'd consider romance with MC is the photoshoot, where it's a forced interaction (you make the choice as the player, but if you're interested in Erynn, you're not gonna leave her hanging here). All the other times are the MC taking a step (or the rare case early on where she makes a move and it's a huge mistake to accept it) and then getting frustrated sexually because she can't reciprocate.
She was a teen meeting new people on a new school, a teen we know turned a lot of heads and grabbed a lot of attention, it's unrealistic to expect that she would just turn everyone away.
Erynn stays behind to try and shut Ethan down, you can argue wether that was the right decision or not, but she was put on the spot and had to make this call in the heat of the moment... then she goes to see him the same day, right after he locked himself in his room and Emily tells her not to.
Even before the recent letter much was said of the effort she put into reconnecting with him, how much she thought about him and wanted him back in her life, on this part the MC is definitely to blame for ignoring her and making as hard as humanly possible to reconnect.
Neither girl thought of him sexually before that day(probably why there's so many scenes of Erynn thinking about how he grew up nicely), he was a little kid for them...
Erynn is slow to progress for 2 things:
1-She's scared to lose her friend, she worries that if they date and it doesn't work out it will lead to a cold and distant relationship, for her this is a real worry, she wants to remain close to him always, so this is something she must take into consideration, the risk vs reward(this was more a thing early on then now, but still a little bit).
2- Her bad experience surrounding sex, she had sex and it led to years of torment... she was left traumatized by the experience, so jumping into bed isn't something she just does.
Every small step of gaining comfort around the MC is character development/progress in her case.
