Marrying a second woman behind your wife's back: is it wrong and can Quran/Hadith prove this?

Salam alaykum. Please note that I myself am not in this position, rather I am in the position of knowing men who say they do "halal cheating"; namely marrying a second woman making the sexual activities with the second wife permissible in islam. I am not knowledgeable enough to do more than to advise them it is wrong to trick your first wife and not take her choice into account or her comfort. However, what I wonder is if someone may be able to cite islamic texts to show that in islam it is actually wrong to hide such a thing from your first wife. I am sure that many of these men would, in knowledge that it is haram or makruh to lie to your first wife, stop having these thoughts. The entire "halal cheating" seems to be a form of self-validation for people who are no better in spirit than the fornicators who have extramarital sex, as they also give in to their compelling desire for lust. I am very grateful for anyone who would be able to provide islamic citations!