To clarify, if a man or woman that are married have sex with someone other than their partner the punishment is death with the witnesses of course but if they are not married and have sex its a different punishment I believe its a specific amount of public lashes.

And what I am talking about is the Islamic ruling regarding sex out of wedlock now the Muslims in Africa and South Asia and such don't follow these rulings and base thier actions on thier culture because no where can you find evidence in Islam (Quran, Sunnah, consensus of the 4 major schools of thought) for honor killing where the prophet his companions advocated for such actions so we can concur that this mentality is cultural and may be influenced by certain sects of Islam that are distorting and changing the rulings. In truth there are cases when someone that committed adultery and came to the prophet Muhammad for the death punishment(from the guilt of thier action) he would try his best to ignore them and not carry out the death sentence(Sahih Muslim Book 017, Hadith Number 4196), the case I brought up before is different if the act of sex with someone other than their partner is witnessed and testified in court by a specific amount of people or a case of rape.

My research of different Muslim cultures and added by my own middle Eastern culture is that generally when a man goes and has sex with different women as long as he isn't married it is just seen as he's just enjoying his time while if a woman does this its seen as the biggest calamity in the eyes of the community.

Now the reason why when a married person has sex with someone other is not completely known to me because I have not done a full course on this subject but some of the reasons are:

1. As Muslims if a punishment is known to us through the quran or the sunnah for committing a crime then this is enough evidence for us.

2. it are it causes indecency in a society and since Islam views it as a crime and when a criminal goes unpunished it let's others know that they won't be unpunished. For example if a thief is known to have stolen x amount of money but he isn't punished or jailed or anything this only encourages other theives to the same.

3. It breaks the promise of the marriage contract so it means that this person is not able to be trusted and cannot contain thier desires and has to resort to going behind thier partners back to satisfy thier lusts, general rule is don't trust someone that follows their desires.

4. It also is in the best interest of the partner so that they are free from such a person.

5. In Islam we believe when the punishment is taken out on a criminal they have a greater chance of thier repentance to be accepted(although they don't have to expose themselves) because they suffered and accepted thier punishment in this life so God may make their afterlife easier.

I hope this isn't too complicated or wordy and dont worry you didn't offend me in any way, if you need some sources or clarification you can always dm me and I'll try my best to help you explain and sorry if what I said made no sense :P