I can't speak as a straight man, as you clearly know, but I can tell you that based upon what women tell me when we hang out, that "guy" friend (unless a gay man or childhood friend that is also ugly) can be problematic.
Simply put, when you two have problems, she will run to him as her escape and shoulder to cry on.
Unfortunately, that shoulder to cry on soon thereafter becomes the dick she leans on.
"1"