Our two lives are like parallel lines - we no longer have anything in common.
Tips
usage
Standard geometry term but heavily used as a romantic / philosophical metaphor in song lyrics and writing: 我们是两条平行线 'we are two parallel lines' = we will never be together. The associated phrase 平行线永不相交 ('parallel lines never meet') is itself a popular Chinese trope for unrequited love or destined separation.