I've always thought that Days was definitely about Nagase and how he is now moving on with a different girl. Love'n'Hate also seems pretty obviously about him, at least to me.
It doesn't sound like this song is about a crush at all, but about a past love who she wanted to love fully but for whatever reason inside of herself she was not able to. Nagase wanted the relationship to get more serious for a long time (hence why he stuck around for 7 years), but its commonly believed that Ayu was the one holding back. I think Love'n'Hate's lyrics express her mixed feelings about that.