You're quoting from an obviously biased reading of Web 55 by someone who wants to prop up Slott's current characterization.
I didn't see anything immature about Peter's actions in Web 55. If anything, it's a sign of maturity to be self-aware and recognize when you are acting in a less than optimum manner.
To quote from the actual text: "This is exactly what I want to talk to Glory about, but now that I'm here...she's so despairing I don't know what to say." In other words, Peter is being empathetic - a sign of being an emotional grown up - and doesn't want to cause his friend more pain and anguish.
In addition, and I know from experience, most men aren't exactly comfortable around women crying over their relationships. I can just see the criticism now if Peter stayed to have a heart-to-heart with Glory: "He's a wuss! He's not manly enough!" Besides, Peter's advice - on the face of it - isn't terrible. Glory is a good person, she knows Eduardo is a criminal so Peter isn't neglecting his duty to warn her, and there's no reason for Peter not to trust that Glory will do the right thing. The fact that she doesn't is what makes this a story - and one with some emotional heft, unlike 99% of Slott's output.
And when people are saying Peter is acting immature in Slott: it's not because he's beating himself up over not giving a friend comfort. Slott's Peter doesn't even realize WHEN to beat himself up. Slott's Peter is selfish and out for yuks and rarely, if ever, stops to think about the consequences of his actions on others - just like a child, who has yet to learn that the world doesn't revolve solely around his/her wants and desires.
In Web 55, Peter is emotionally mature - he is aware of others' feelings. And he scolds himself for not acting better. But being mature doesn't mean being perfect and never, ever making a mistake. Being an adult means you have the maturity to recognize WHEN you made a mistake. This is as far from being a basketcase as possible.
Slott's Peter, on the other hand, is a perpetual prepubescent emotionally (with the hormones of a teenager, but not going there). Even though Slott himself has pegged Peter as 28 years old - 13 years since the spider-bite at 15. So really, no matter how "relatable" Marvel wants Spider-Man to be to younger readers, his current behavior is starting to look ridiculous.
But once JMS left, and after the retcon of the marriage and the return to the 1960's/70's status quo, Peter was more or less at square one. So yes, he was immature, but he was also an adult for a great period of time. I mean, he was also with the Avengers (Remember that.).