All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
First of all, we thank you for trusting us and writing to us.
If that man did what you mentioned, then he has indeed committed a heinous act and an abominable sin that is contrary to the teachings of his religion. Islam commands the Muslims to shun immorality and stay away from adultery. It is indeed an evil act towards someone who had done good to him. This shows that he is a wicked person, as a kind person recompenses good with good.
Nonetheless, what that man has done does not change the fact that this woman is your wife and that the child is your son.
On the other hand, by this act, your wife has committed a sin against herself and against you.
If you left that man with her in your home, then you are also to blame, as you were negligent in this regard. It was most likely that letting them live together would lead to what happened.
It is for this reason that the wise teachings of Islam set barriers to preserve the Muslim family and maintain its honor, so it forbade a man from staying alone (in seclusion) with a non-Mahram (marriageable) woman because that is a reason for temptation.
Prophet Muhammad said, "None of you should stay in seclusion with a woman, as their third would be the devil.”
We take this opportunity to ask Allah to bless you by embracing Islam. We perceive that you have a sound mind that will lead you to goodness and which will be a reason for you to embrace Islam, and hence you will open the door of goodness for your family.
We hope that you will benefit from the following fatwas about Islam: 81979, 88906, and 88051.
Allah knows best.