|If my memory is correct, he only appeared in 13 episodes, and all of them were in season 1. The last episode he was in, would have been "The Exor-Sis".|
I've never heard of the exact reasoning for his departure, but it could have been a number of things. Rachelle Lefevre also left at the end of season 1, along with Jane Gilchrist (who played the lunch lady), and i'm sure a few others. Could be a scheduling conflict, could have been budget issues, or even a creative shakeup. With secondary characters like Hugo, they often run out of ideas on how to move the character forward. Instead, they just replace the character with a different one. So that could also be the case.