I think the best way to convey something you don't know how to say is to put it this way
"I don't know the right words to use - so I'll say it directly. I BADLY want to keep this job but I even more so can't be 'on call'" .. you can explain to them that for you personally you need separation between work and personal life."
"I don't know the right words to use - so I'll say it directly. I BADLY want to keep this job but I even more so can't be 'on call'" .. you can explain to them that for you personally you need separation between work and personal life."