Cavallo hopes more professional footballers will follow his lead and publicly announce that they're gay.
"I know there are other players living in silence," he wrote on Twitter. "I want to help change this, to show that everyone ... deserves the right to be their authentic self.
"It's astonishing to know that there are currently no gay professional footballers who are out and actively playing, not only in Australia, but around the world.
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"Hopefully this will change in the near future. I want to ... let other players in my situation feel that they're not alone."
The 21-year-old said growing up he "always felt the need to hide myself because I was ashamed."
"Ashamed I would never be able to do what I loved and be gay," he wrote.
"Being a closeted gay footballer, I've had to learn to mask my feelings in order to fit the mould of a professional footballer.
"Growing up being gay and playing football were just two worlds that hadn't crossed paths before.
"I've lived my life assuming that this was a topic never to be spoken about."
Adelaide United coach Carl Veart said Cavallo, who has played 19 games for the Reds after playing nine matches for Western United, has "shown incredible courage to be one of very few professional sportsmen to be this brave."
"I have nothing but admiration and support for him, as do all the players and coaching staff," Veart said.
"I want all my players to feel comfortable and happy being their own person, on and off the park.
"For Josh to be the best he can be and get the most out of his career, he needs the freedom to be himself and I fully support him."
Melbourne man Cavallo said his Adelaide teammates and coaches had been like a family to him, but he grew weary of having to swerve "normal locker room talk" about players' love lives.
"I experienced a type of sadness and depression I don't wish on anyone," he said on a Network Ten website.
Cavallo said Thomas Beattie, a former youth player for English club Hull City who came out in 2020, had been a "role model" in helping him on his journey and hoped their example might help change things for other young, gay men in sport.
"Statistics show only 33% of young gay men play football in comparison to 68% of young straight men," he said.
"That's a lot of wasted young players missing out -- players that could be very talented, but who don't fit the norm.
"Perhaps we can play a part in saying that football accepts everyone -- that you are all welcome?"
Information from Reuters was used in this report.