Stein used to play water polo for Charter Oak and said he was asked by the head coach to help out in May 2011. He only makes $2,500 a term and said the lawsuit is "not about the money" but standing up for his rights and those of other LGBT teachers and students at the school.
Stein said his immediate reaction was to leave the school, but his teenage daughter Devynn talked him out of it.
"She said, 'No, Dad. If we leave, they have won,'" said Stein. "She taught me a lesson."
Since then Stein has received support from others at the school.
"One teacher actually apologized to me," he said. "He worked for the same school district in 2003 and had similar problems and knew he was being treated differently because he was gay. Instead of standing up and fighting, he had left."
According to the Los Angeles Times, which first reported the story, that male teacher filed a sexual orientation discrimination complaint saying he was harassed by an administrator.
The district said it did a "thorough investigation," according to the Times, and there was nothing to substantiate the claim
The day the lawsuit was filed, students and parents protested outside the court on behalf of Stein, according to his attorney Brad Kane.
A new Pew Research Center poll released this week found a sharp increase in support for LGBT teachers.
"While just 25 years ago, 51 percent of Americans said school boards should be able to fire teachers purely based on their sexual orientation, that number has dropped to just 21 percent today," said advocacy the group, Think Progress.
Gay rights groups like GLAAD were supportive of Stein.
"It's time school administrators go on record and answer the question: Would this even be an issue if Mr. Stein were straight?" said GLAAD President Herndon Graddick. "Keeping homophobia out of America's classrooms and creating safe learning environments for students should be the school's focus, not decades-old photos."
Stein said that he has been a good coach, even refusing to lead the girls' water polo team to avoid accusations that he favored his daughter who is one of the players. He said he had never been disciplined before and never had an opportunity to take down the photos or address the real issues behind the firing.
Despite losing the coaching position, Stein still goes to practices every day and was just elected president of the booster club, helping the team raise $15,000 this year for the aquatic program.
"Right now, with the Republican primary and so many people in the news saying we have to protect the family, no one sat there and said how it would affect my daughter and my family," said Stein, choking up on the phone.
He and his partner Hugo Horta have had a tumultuous time in the last few months. His adopted 7-week old Tuolumne Horta-Stein, the daughter of a drug-addicted mother, nearly died at birth and has just arrived home from the hospital.
But that won't deter him from seeking justice from the school.
"We have these laws in California and if no one enacts those laws, things are not going to change," said Stein. "The social climate in that district is toxic. Gay students have come to me and said they are afraid if they do it to me, they can do it to them. I need to set an example."