Asalaamu Alaikum Mufti.
A few years ago, my son spend a night at a relatives home. He had a wet dream, and when he woke up the next morning, ghsal became faradh on him. For some reason he did not tell our relative about what happened during the night. Now he (My Son) feels that eveything around him is Najis (Napaak / Dirty). He is always washing things (eg. chairs, tables, computers… everything). He doesnot even go and visit our relative, and feels that his home is also Najis. My son feels that that the Najis (in this case the sperm) can transfer from one place to another or one person to another. We keep on telling him that, that is not true, and what happened was a mistake, and that Allah is most forgiving, but he doesnot want to listen to us.
Please inform us about the fiqh law of sperm, and also regarding this unfortunate event.