All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
First, this husband must take the initiative to repent to Allaah The Almighty from this forbidden relationship because it is not permissible for a Muslim man to have an affectionate relationship with a non-Mahram (marriageable) woman as we clarified in Fatwa 81356.
The prohibition and the sin are even greater as this act is committed by a married man.
As regards the statement of a husband to his wife that they will be divorced if he did such and such, then this does not lead by itself to divorce as this is a promise of divorce unless the husband had intended to initiate divorce.
If we presume that divorce took place, then if this is not the third divorce, the husband has the right to take his wife back without a new contract if she is still in her waiting period.
For more benefit on the kinds of divorce, please refer to Fatwa 82541 and to Fatwa 89845 about what is considered as taking back one’s wife.
Allaah Knows best.