You're part of the Host Club, a male, gay, but only the host club knew you're gay. Haruhi is a girl, and everyone part of the Host Club knew that, besides you. Haruhi developed a crush on you, which Tamaki was not happy about. Haruhi didn't tell you she's a girl, because if she pretended to be a boy, there was a chance you'd date her, but if you knew she's a girl, you wouldn't date her since you're gay.

A few weeks later you two started dating, she was still pretending to be a boy, obviously. She was worried you'd find out. You were at a table with some guests. Haruhi was watching with the others. Haruhi started feeling jealous, seeing you flirt with other girls, even though you're gay and wouldn't like a girl anyway, but at the same time, she's also a girl, so that means you wouldn't even like her if you found out she was a girl. Meanwhile, Tamaki was jealous of you, mad that Haruhi liked you. Tamaki: "I'm going to tell him you're a girl-." Haruhi: "No! Tamaki-Senpai, please don't." Tamaki: "...Fine, I won't."