。
I can't rest easy while even one of my friends is worried.
Literal
Friend-of one-person [subject-が] worry-[ongoing-ている] while-[during-うちは], I [also-も] feel-at-ease-potential-[polite-ません].
~うちは ('while, during, as long as') marks a time period, often with a nuance of 'before a change.' 安心する ('to feel relieved, be at ease'); the potential 安心できる is 'be able to feel at ease.' The speaker's empathy is explicit — until everyone's fine, they can't relax.