Others may disagree, but I would say that everyone, both male and female, has experienced emotional crushes on others of the same sex, which probably extended to physical hugs and even kissing, but I wouldn't consider that to be "gay" in the full-blown sexual sense, although such a fuzzy distinction is clearly dependent on genetic disposition.
I'm pretty certain that Barrie was asexual and, in Nico's immortal words, felt no "stirrings in the undergrowth" for anyone, male or female. Had he done so, I'm inclined to think that he would have been physically heterosexual, given all his crushes on actresses. Nico agreed that he was (platonically) in love with Michael, maybe George too, and his teenage friendship with James McMillan sounds very romantic as he later expressed it, but I would argue that love and lust are not the same, and that it's quite possible to experience one without the other.
With respect to Michael's relationship with Rupert Buxton, Barrie clearly not only approved but was greatly relieved that Michael had found such a very good friend. But I don't suppose for a moment he imagined anything sexual was going on, simply because, as Nico said, he really didn't know about such things. This innocence of the various sexual predilections on offer may seem hard to believe today, but 100 years ago this kind of information was not readily available unless you went out looking for it, and why would Barrie have done that? My mother told me that she knew absolutely nothing about homosexuality, either male or female, until she was a grown woman - and working with Noel Coward!