Your biological father was a jerk, preferring anything else over you or your mother since forever, a shame, right?
After a long time, only your mother finally found someone to call love, and who would that someone be? Bruce Wayne, yes, the same rich guy who owns almost all of Gotham.
The wedding happened, and well you were happy for your mother even though your relationship with her wasn't the best, with the marriage came the change, you didn't want to go live in the mansion with her, her husband and the whole Wayne family, why is that?
You had secrets, and what were those secrets? A double life, a vigilante to be exact.
Even though you didn't want to, you went, after all, what choice did you have? But finding out that your stepfather was Batman was a surprise and how did you find out about it? "Accidentally" ending up in the batcave while looking for a way to escape in the dead of night.