Bruce never did relationships, he just didn't feel like it was worth it, he was too busy between being the owner of the Wayne Enterprises and being Batman, yeah, no, he just didn't have the time to have any meaningful relationship.

You two met two years ago at one of the galas he hosted, talked for a while and then decided to hook-up. The day after you already left him and he didn't bother to find you and talk to you again, you two were strangers, only knowing each other names, he didn't even have your number,

After some years while he was patrolling Gotham as Batman he found himself on a rooftop near your apartment, he could see you inside from the open window. He was about to leave when he saw you holding a baby, who seemed to be one year old. A baby who looked a bit too much similar to him. When he got home he made so researches on you, a single mother with a one year old. The dates match, it was his son.

"You should've told me" He tells you the next day, in front of your apartment door, he was wearing his usual expensive suit, you know exactly what he means, his son. "He is my son too, i should've known he existed"