Second couple

Are we really giving real life advice to ppl based on assumed behaviours within a friendship which is only explored in a very limited way and used as a plot device for the main couple's relationship? You can speculate, but surely unless you make an extensive analysis on the matter you can't quite turn this into a life lesson
Sometimes it's valid enough to just say that we wanted more of a side character and that we're coping with that disappointment.

Well yes! Even though we see a very small portion of these characters interaction for the main chunk of the story, it is not healthy and if someone is treating someone else like this, it’s probably not healthy! Like everyone else knows their friendship better than obviously however, sometimes you need third advice. I’m not arguing for the disillusionment of all friendships, but sometimes you don’t know something is unhealthy until you’re outside looking in.

I mean, also we did want more of the side character. He is interesting character, but he’s getting fucked by everyone, including the writer.

Extremely limited, circumstancial information and a vague conclusion of "probably not healthy" isn't sufficient reasoning nor evidence based on which to pathologize real life relationships.
I hope you understand the whole premise of your advice is false.
If you'd like to genuinely help yourself or others out, I'd suggest actually making an extensive analysis using real life examples, based on the jumping-off point of your choice as presented in a oiece of fictional media. Which is really interesting when done right! Life just isn't black and white as to be able to surmise the health of a relationship and our due course towards it from something like this..
If you just want to rant just for the sake of it while reading an entertaining story, then ofc that's fine and no need to try and force a cautionary tale to it.