So it's not surprising to me if John was intrigued by homosexuality or experimented with it.
Yeah, I definitely agree with this. John, as was previously mentioned, has always come off as 'sexually confused' to me, so I think that it might have been possible that he experimented with it for personal reasons - because he was frustrated with his current relationship, because he wanted to try something different, because he was just curious, perhaps. I wouldn't put it past him, really - I don't think he'd be very squeamish about anything having to do with sex
, and if he and Brian did actually end up doing anything (and I do think this is debatable, I was just citing the Spanish vacation as a possibility), it was Brian, after all, someone he knew and trusted.
I think if John was privately intrigued by homosexuality, it would make sense that he would write a song about it with Brian in mind, as the closest person to them who was gay. (And then disguise it, of course, by doing some switching of pronouns, because the other way around could be potentially disasterous at the time).