Danny fell in love with Bruce Wayne in college. If he was completely honest with himself he didn't even know about Gotham or the outside world by that point, he just knew he had to get away from home for a while and complete his studies.
He didn't expect to run into a playboy billionaire who was supposedly very dumb at his college; Danny knew better, he could tell the difference between the act and the real Bruce, someone truly thoughtful, caring and very smart, but no one but him noticed so he didn't say anything.
They became very good friends despite their obvious latent crush and on graduation day Danny was about to confess when he got a call from home asking for help with the GIW. The halfa had no choice but to say goodbye not wanting to get Bruce in his mess.
When he returned to Gotham months later he learned that Bruce was gone, his butler informed him that he would be back but didn't know when and the halfa returned to Amity in disappointment. He decided to take over the Realms for a while and distract himself with all the responsibilities he had been avoiding.
Years later he was called for a college reunion. Danny was very nervous, he hadn't kept in touch with the outside world but his core was still glowing for the billionaire, he wondered if Bruce would remember him.
Despite his plan to confess his old feelings (and pretend they no longer existed), Danny was unable to do anything but look at Bruce who greeted him with a smile and a small child at his side. The halfa grimaced, maybe he was married?
Bruce seemed excited to see him again and exchanged his contact, asking him not to go off the radar again, the halfa felt a little guilty about it. They continued to communicate over the years. Danny noted with amusement how his crush kept adopting children and calling him for a dinner at the mansion.