He lost interest in Reddit at some point and just got really flaky... not turning up for work and shit like that. Think he was going through depression at the time and there was a bit of drama around all that.
EDIT: It's a real shame he and Alexis Ohanian didn't get along better... it seems that thay could have made a great team, with him being the soldier and Ohanian the diplomat in a fight against govts/corporations (SOPA, TPP, etc) impinging on our freedoms online.
http://www.reddit.com/r/reddit.com/comments/1octb/reddit_cof...
It was decided that he would 'merge' with reddit, but the reddit guys described it as him turning up one day and them having to deal with it.
He was flaky and got fired.
Yes theres lots of other details but thats the gist of it