The Catholic Church certainly does not interpret the passage to allow remarriage in the even of adultery if a valid, insoluble sacramental marriage is present. There is thus no exception. Saint Paul’s epistles make clear that a remarriage attempt following a valid marriage is adultery, if there is any lingering confusion about Christ’s meaning in the Gospel.
The dispute in this thread is what exactly is meant by this passage; it is a dispute of semantics rather than theology. The Challoner notes are one eighteenth century bishop’s interpretation of the particular issue address by the passage. In addition to Challoner’s, my interpretation is that Christ is clarifying that an invalid marriage may be dissolved, and Bob Crawford’s position is that infidelity is prima facia evidence that a marriage is invalid.