Everyone being gay is a trope not only in BL manga, but in slash fiction in general. Rather than wondering whether it's realistic or not, it's far easier to handwave it and just understand that the author wants to write about BL couples and it's easier to include multiple in one series than to...
And while no one was looking, the final chapter was typeset. It's really a wonderful conclusion. I know that I was satisfied. Feast your eyes and your hearts fellow readers: https://imgur.com/a/7LOYYhb
(For anyone who's curious, that link is the one provided in Imey-chan's blog. For some reason...