"There's a girl here at the Tower," she replied, "her name's Batgirl and she said that you know her." She paused for a few minutes and added, "She also said that she needed to talk to you ASAP and wanted to meet you somewhere where you could talk to her."
Robin couldn't believe it. Barbara Gordon, Batgirl, was here. The last time he saw her was the day he left Gotham City.
He remembered that day well. It was also the last time he faced the Joker. Batman and Batgirl were facing him on top of city hall. Robin arrived just in time to save Batgirl as Joker knocked her from a building. Things were growing rocky between him and Batman as Robin was growing tired of living under Batman's shadow. This was the night that ended everything. And Batgirl stood by Batman. To make matters worse, Batman figrued out who Batgirl was, put her in harms way, and never told Robin.
Batman told him,"It wasn't my place to tell you."
Robin excalimed" But it was your place to put her in danger!"
Batgirl insisted she voluntered, but Robin was so angry he didn't beleive her. Then Robin said one of the two things that evening that he wished he could take back," You think you did. You don't know him like I do. He manipulates, pulls strings, anything to get what he wants."
"I thought we had the same goals," Batman said.
Robin starred Batman, his friend, his adoptive father, and told him teh second thing he regreted, " Things change. I've changed. The game's over, Batman. I quit."
Then before Batman could say anything more Robin kncoked him to the ground with a swift left hook and stormed off.* It wasn't more then a few months after that when he joined up with the Titans[/I]
Robin knew Starfire was waiting for his response and so was Batgirl. He could dwell on that past memory too long.
"Tell Bar... err Batgirl to meet me at the Dixon Observatory. I'm on my way right now, Star."
Robin put his communicator away pulled out his grappling hook and swung down to the alley below where he had hidden his motorcycle. Then he hclimbed on the cycle, and sped off towards the Titans Tower.
* Robin's memory is taken from the Batman: The Animated Series episode "Old Wounds", so if nobody minds, Robin is Dick Grayson.
I think there were plenty of hints towards that in the series any way.