had something similar before back in the states, but nowhere near as bad. are you married? if so, just tell him to quit if it's too much. you can support him until the next job.
also, stay positive and be very supportive. a lot of times, personality may determine how much stress you get. try to talk him into looking at things differently from before. i used to be very hard on myself and held high standards but that only made things worse since you can't do everything by yourself anyway. then moved here. different job. half the pay from before. but much less stress.