Glynda secretly loved the antics all the kids got up to. She put up the facade of annoyance, but she wouldn't still be here if she didn't like it. She would never have an affair with a student, but there was one teacher who also acted like a child. Oobleck. He was always hyper, came up with preposterous plans, and was always getting into trouble, though by this point he was adept at also getting himself out of it.
Oobleck knew Glynda liked his antics. In fact, he specifically brewed a stronger blend on days he knew she would be around. He also loved working with the kids, though he enjoyed it more because they felt like freinds, rather than the more motherly feelings Glynda had. Oobleck and Glynda made a great pair for teaching, Oobleck trying to sprint through the material, and Glynda slowing him down just enough for the students to actually understand what he was saying.
Plus, they loved to play pranks on each other. Glynda would put sedatives in his coffee before his final class so he would go extra slow, Oobleck would find clever places to hide her riding crop suggestively, making sure it was nowhere that a student would see, of course.
Then one night Qrow was reporting in, and had brought some alcohol he had been brewing in his free time. Ozpin refused to try some, saying he hadn't had alcohol in 30 years. Seeing how Qrow was casually drinking it from his flask, Glynda and Oobleck each tried a single shot glass. From that point until the following morning neither of them have any memories. Qrow told them all about it though. He told them about their drunken singing and dancing, their dual confession of love, and their sloppy kissing, ending with Glynda leading Oobleck into the elevator. He said they were fortunate there weren't any students around. When they woke up in Glynda's office the following morning they had each other's clothes on. They awkwardly swapped, not looking at each other or saying anything.
After hearing the story from Qrow, they both said that it was just alcohol induced stupidity. Nothing more.
Both of them knew the other was lying.
They avoided each other for a couple days, not wanting to have an awkward conversation about it. Finally Oobleck needed some paperwork from Glynda.
He entered her office.
She looked up at him.
He kissed her. He hadn't planned to, but as soon as he saw those green eyes he couldn't resist. They pulled each other close and kissed until they needed to breathe. He quickly tidied his shirt and grabbed the paperwork, winking at her and saying he'd see her after class.