Disclaimer: Oh yes, I own KHR, which is exactly why I'm writing a fanfic about it instead of putting it into the actually story. Totally makes sense.
Completely and Undeniably
Tsuna knew it was official. The Vongola was completely and undeniably gay.
The first relationship to start was Spanner and Shouichi. However, this was understandable as they spend god knows how many hours in an office with each other. Not to mention they knew each other since junior high school and shared the love of robots with each other. A geek hooking up with another geek. Nothing out of the ordinary.
The next 'relationship' that came to light was, surprisingly enough, Squalo and Xanxus when they were found unceremoniously screwing each other on Tsuna's desk after his Inheritance Ceremony. Well, they were in an assassination squad where women were scarce and they were part of the mafia so they couldn't have had much experience with women so yeah… that explained it. Tsuna had to use two weeks' vacation worth of brain bleach to remove the sight of this relationship, though.
Third couple surfaced after the Arcobaleno curse was broken. Reborn was an adult and after not having screwed a guy, girl, or anything since he had become a baby, he immediately jumped on the nearby Colonello, dragged him to the nearest enclosed space and began to stuff the donut hole. Tsuna should know. The room Reborn dragged Colonello into was his bedroom. He was shoved into the closet so he wouldn't disturb them.
Gokudera and Yamamoto were next. Candy that Chrome made got mixed up with candy from man-hungry marriage seekers. They were found in Yamamoto's room, tangled in sheets and a zebra lounging in the bathroom. Tsuna didn't even want to know.
Lambo began to have a schoolboy crush on Fuuta. It was long suspected by many that the boy was gay when he was about twelve. Lambo still bathed and slept with I-Pin, showing no signs of interest in any women at all, not even looking at their bodies. When Fuuta asked if Lambo wanted a relationship with anyone, Lambo looked at him and blushed. Fuuta later did a ranking and nearly had a heart attack.
Hibari's first time was taken by Ryohei when they were both drunk enough, and went on a few dates afterwards, which ended when Hibari had sex with a Mukuro disguised as Ryohei. Ryohei attacked the illusionist and Hibari decided that such interaction was too much crowding than he could handle. Ryohei was still trying to win him back.
Mukuro picked new recruits that he thought had 'potential' as an illusionist, choosing to mentor Fran from the Varia while simultaneously fucking him, drugging Hibari on the side if he needed a quick one night stand. Hibari beat him, but Ryohei would attack him until he was near-death.
Bel had gotten quite chummy with the now-adult Mammon, who was quite peeved at being the 'girl' in the relationship when Bel forced him to cross-dress. The picture of the Arcobaleno in a scanty dress spread through the underground like wildfire.
Tsuna's Outside Advisor, who had inherited the title from Iemitsu, Basil began to go out with Lancia, who was making a living as an independent assassin who specialized in Storm Flames. It turned out that Basil had a crush on Lancia as a teen and eventually wore the man down.
Tsuna recounted all of these relationships and wondered why the entire freaking Vongola was becoming gay. He was reading Primo's journal one day and was fairly shocked to find a conflicting entry on whether he should accept Cozarto's confession or be with G. Tsuna nearly broke his office with the extent he freaked out.
Tsuna concluded that the Vongola was completely and undeniably gay.
Of course, he was included. Why else would he be lying with Enma, a male, on a bed, doing unspeakable things?