Charles Ellicott Commentary 1 Corinthians 7:11

"(but should she depart, let her remain unmarried, or else be reconciled to her husband); and that the husband leave not his wife." — 1 Corinthians 7:11 (ASV)

But and if she depart.—Better, but if she has actually separated. These words, from “but” to “husband,” are a parenthesis, and the concluding words, and let not the husband put away his wife, are the completion of the Lord’s command given in 1 Corinthians 7:10. The Apostle, in case such a separation should already have taken place, anticipates the difficult question which might then arise by parenthetically remarking that in such a case the woman must not marry again, but ought to be reunited to her former husband.