It was Luke's suggestion to break up Brenda and Dylan in 90210...
I bought the season 3 DVD pack of 90210 and watched the season finale with the commentary one. The executive producer Chuck Rosin was commenting on the season finale and he mentioned that at the end of each season, he brought the cast in one at a time to see if they have any suggestions and to find out what they would like to see.
He said at the end of Season 2, Luke came in and said that he thought it would be cool for Dylan to get involved with Kelly. Chuck spoke with the writers and other producers and everyone went for it so they made it happenen.
The long term goal was to get Dylan back together with Brenda but I assume because Shannen Doherty left the show, it never happened.
I just thought that was kind of interesting. I never had heard that.