What's the Name of That Book??? discussion

I read this series about 5 years ago now, from memory it was quite a long series with 6+ books. Based around a group of 7 or so boys that befriend a girl from school, they seem a little odd though as they are always disappearing to go do secret things. Later she learns that they are part of a secret society headed by their “teacher”. She is brought into the fold and each book kind of shows another one of the boys falling for her, and her reciprocating. From memory one of the characters is named Gabe

Is it the Ghost Bird series by C.L. Stone? It seems to match well with what you've described.

Yes! Thank you so much!

Introductions for the link