Adam Clarke on Romans 7:3

So then, if, while her husband liveth - The object of the apostle's similitude is to show that each party is equally bound to the other; but that the death of either dissolves the engagement.

So - she is no adulteress, though she be married to another - And do not imagine that this change would argue any disloyalty in you to your Maker; for, as he has determined that this law of ordinances shall cease, you are no more bound to it than a woman is to a deceased husband, and are as free to receive the Gospel of Christ as a woman in such circumstances would be to remarry.