don't see how we could possibly believe that Erynn wasn't in a relationship with Ethan. In Episode 5 we learn she went to the prom with him, she still sees him regularly because of work, he calls her babe (though that could be because he wanted to irritate the MC), and Ethan said that he fucked Alexis when he and Erynn were a couple.
Just because she went to the prom doesn't mean much, in the end she could just have said yes because Ethan was extremly persistent and the MC wasn't there anymore.
Her reaction, where she sights and said don't remind me could imply both.
That she made a large mistake with Ethan, which she regrets, than the question is why would she continues to see him.
It could also mean that it was a very unpleasant evening for her, with a persistant Ethan and she was happy when it was over. While the prom she wanted, was a memorable/romantic evening for her and the MC.
For the babe thing, i'm pretty sure it was just Ethan riling up the MC.
For the Alexis fucked Ethan accusation.
Yes the most most obvious answear she was in a relation with him.
On the other hand, we really lack context there. If she was in a relation with him and ever belived Ethan, i don't think she would still be friends with Alexis, ur best best friend cheating with ur lover is pretty much the ultimative breach of trust.
If she didn't belive him, that should ruin her relationship with Ethan to such a degree, that i would find it hard to belive that she would still be friends with him.
Additionally i find it hard to belive that someone which so obsessive, that she still want to give a answear to a 5 year old confession, would start a relationship with the dude that was always hostile to the MC...
Well maybe i simply overthinking it and don't want to see the most obvious answer, as it would close of Erynn as a LI for me, while i still hope that the Nyx will make her a top runner in the competition.