I thought I'd post additional bio information for what happened to Dean while in Rhydin because his story deviates a little from canon Dean.
Dean arrives in Rhydin shortly after Jo and Ellen die (Episode 5x10, Abandon All Hope) and returns home after Lucifer is imprisoned in the pit and Sam returns from hell (Episode 5x22, Swan Song).
It goes something like this...
After an encounter with the demon Meg, Dean is thrown through a mirror into Rhydin, where he meets and falls in love with Quinn Benoit. Torn between his love for Quinn and his devotion to his brother Sam, Dean attempts to return home, but his soul is torn in half, and part of him stays in Rhydin, while the other half returns home to Sam.
The Dean that returns home to Sam continues with the quest to kill or capture Lucifer, as seen on the TV show, while the other half tries to make a life for himself in Rhydin.
Dean and Quinn run into some problems with demons while in Rhydin, and Dean finds out some things about Quinn, which I will not reveal here, as that is part of Quinn's story, but which lead him to believe that she is safer and better off without him. In spite of that, he proposes to Quinn and tries to make a new life for himself in Rhydin, but tormented by memories of hell, overcome with grief over Jo's death, and feeling lost without his brother, Dean's drinking problem gets out of control.
Dean meets another hunter named Greg and befriends him and Spade, but is drawn into their problems when it's revealed that Greg is demon spawn. Dean offers to help, but Castiel, the angel who pulled Dean out of hell, finally locates Dean and tells him he doesn't belong in Rhydin and that he has to return to Earth. After a confrontation with Abaddon, the demon who fathered Greg, Castiel takes Dean and Greg back home and returns that half of Dean's soul to his body after Lucifer has been returned to the pit.
From this point, our story deviates from the canon story, as Sam and Dean are actively hunting Abaddon, who is one of many demons struggling for control over hell, which is now in chaos. Castiel recently informed Dean that Greg killed himself, which adds to Dean's feelings of guilt and remorse, as well as his loneliness in knowing he can never really have a normal life, no matter how badly he might want it.
And that about brings things up to speed. I know it's complicated. Feel free to PM with any questions or post in the OOC Guestbook Thread. And thanks for reading!