§ 171. When divorce denied, although adultery proved. In either of the following cases, the plaintiff is not entitled to a divorce, although the adultery is established:

1. Where the offense was committed by the procurement or with the connivance of the plaintiff.

2. Where the offense charged has been forgiven by the plaintiff. The forgiveness may be proven, either affirmatively, or by the voluntary cohabitation of the parties with the knowledge of the fact.

3. Where there has been no express forgiveness, and no voluntary cohabitation of the parties, but the action was not commenced within five years after the discovery by the plaintiff of the offense charged.

4. Where the plaintiff has also been guilty of adultery under such circumstances that the defendant would have been entitled, if innocent, to a divorce.