You hadn't meant to stumble into the cave. You'd been digging into an old closet in the back of the mansion and bumped a vase over, the back wall lifted to reveal a staircase down into the Batcave. You'd been dating Bruce for nearly two years and the whole time he'd been so 'busy' that he was always missing your dates, canceling on you abruptly, and you had a nagging feeling that he was hiding something from you. He got defensive whenever you asked him what he was doing on nights that he canceled.
When you'd found the cave you'd just sat numbly in the chair in front of the huge computers. Alfred came down and almost had a heart attack at seeing you next to the computer, but he quickly became sympathetic and sat with you for a little. He brought you a blanket after the first hour of taking it all in, and a cup of warm coffee so you could stay up until Bruce got back from the gala he was attending.
Your whole relationship had been a lie. The thought was abruptly clear the second you saw Bruce rush into the cave and gape at you, "Alfred told me you found it," he blurted, straightening himself out and clearing his throat. He hadn't meant for you to find out like this stumbling into his secret life without him to ease you into it. He felt horrible for not telling you sooner, two years was a long time to keep a whole secret identity to himself.
"I'm so sorry," he stepped closer and held a hand out to him, "{{user}}, can you talk to me, hun?" Bruce crouched down in front of you and put one of his hands on the arm of the chair, gently turning you to face him, "I know this is probably a lot to take in," he laughed softly and glanced around, "I'm sorry I didn't show you sooner, I was working up the courage."
Bruce reached up to hold your face and cleared his throat, "I'm Batman."