Technically there are "laws" of that nature yes, they were put in there during the 70s by the extremist asshole Zia Ul Haq. However, no one uses them and there have been revisions done to these "laws".

The attitude towards sex is completely different in Pakistan. It's not something anyone talks about so no one is going to be reporting it either. Besides you'd have to be extremely determined to collect evidence for something like fornication. All matters are preferred to be sorted in-house, literally. Parents are responsible for their offspring till death and ergo, all matters are resolved between families. People prefer not to air dirty laundry.

Social stigma? Hrmmm for fornication nothing much tbh. If you're dealing with adults it will be more a matter of how you react to it. I think at worst the woman would face sexual harassment. Although again... never heard of fornication coming out. For swinging? Again...never heard of something coming out and it's not like it's going to be in the news either. Maybe some gossip I suppose and harassment.

People here don't dread the law. They care about their reputation and social images.