He said: "This has been a difficult decision but I have to put my wife and family first.
"It has been a privilege to be involved with this club, I've met so many fantastic people, I will miss it greatly and am saddened to leave."
He continued: "As relocation to Devon is not, unfortunately, an immediate possibility, I need to return home to Scotland whenever the club can release me."
The club's board have said they are currently in the process of determining the best course of action to replace Stewart, and expect to make an announcement on the matter shortly.
Source: BBC Sport
Source: BBC Sport