Nah, I kinda see the vision and the logic here.
- Seven + MC had 10+ years long co-dependent relationship; music was the 2nd thing Seven used to self-validate and self-identify. The only other grounding point for them was their mom, I assume.
- MC and friends 'ditch' Seven, from 7's perspective robbing them of 2\3 pillars of their world. Cue identity crisis, not an insignificant amount of resentment.
- Some ppl hate their ex-spouses for YEARS after the divorce. For 7 it was essentially that, because they lost a good chunk of what they thought was their identity. Is them not processing it healthy? No. Is it realistic? Yes, because people process emotions differently; some still hold the grudges from high school when they themselves are in their 30s. Not everyone practices mindfulness. Does 7's childishness irk me? A ton. But I treat it as.. you don't have to like all the characters in a book for a book to be fun. Some are there for you to hate them.
Imo, the problem is not 7's character but the way the conflict itself was handled. I do think Amy fumbled A LOT when she pre-defined MC's stance\behaviour in this conflict, because no matter what MC ends up being a spineless pushover, and for some MCs it makes zero sense? Certainly doesn't fit mine. Imo, it would've been wiser to let us pick'n'choose from several possible conflicts that broke things up, like... 1) making 7 a backup scandal for meek or fame-driven MCs 2) MC being neglectful for cold MCs 3) MC or 7 having an addiction 4) MC starting to get uncomfortable with co-dependency... etc.