A.T. Robertson Commentary Romans 7:3

"So then if, while the husband liveth, she be joined to another man, she shall be called an adulteress: but if the husband die, she is free from the law, so that she is no adulteress, though she be joined to another man." — Romans 7:3 (ASV)

While the husband liveth (ζωντος του ανδρος). Genitive absolute of present active participle of ζαω.

She shall be called (χρηματισε). Future active indicative of χρηματιζω, old verb, to receive a name as in Ac 11:26, from χρημα, business, from χραομα, to use, then to give an oracle, etc.

An adulteress (μοιχαλις). Late word, in Plutarch, LXX. See on Mt 12:39.

If she be joined (εαν γενητα). Third class condition, "if she come to."

So that she is no adulteress (του μη εινα αυτην μοιχαλιδα). It is a fact that του and the infinitive is used for result as we saw in 1:24. Conceived result may explain the idiom here.