What is the ruling on an agreement between a married man and a married woman to marry in the future, and abandoning a love affair that was on the verge of leading to adultery, seeking thereby the pleasure of Allah, and will they be rewarded for that?

The two questioners have done well in avoiding adultery, and may Allah reward them with goodness. They must stay away from any illicit relationship and prevent their hearts from becoming attached to each other, because that is the beginning of falling into what is forbidden, as confirmed by the words of the Prophet, peace and blessings be upon him: "The son of Adam has his share of adultery written upon him..." They must turn their hearts away from what Allah has forbidden and stop praying to be united in marriage, because that is a prayer for sin. The Prophet, peace and blessings be upon him, said: "The supplication of any one of you is granted as long as he does not supplicate for a sin or for cutting off ties of kinship." Let each of them know that Allah will compensate them with something better if they obey His command.