The way I see it is that it depends on the spiritual stage of the couple. Remember we are not robots programmed to act in a such manner. There is no program/software put in us to behave only in such particular way.
Giving example based on original topic here. One couple who are amritdhari but spiritual Jeevna is at let say beginner level. They believe issue like eating outside or sexting between them is ok. This is because their inner mind (spiritual level) does not make them think that it is wrong ‘yet’.
Now another couple who are practicing Sikhi at high spiritual level and their mind says that refrain eating outside and indulge in any sexting. That is their gut at oriented lifestyle.
They both are Sikh couple at different spiritual stage. There is no quick fix to make the young couple think otherwise, unless they advance to higher spirituality with help of sangat and discipline.
Now you will also see folks following rules such as above - same example of refrain from eating outside etc etc.. but the only negative part is that they are doing it without their inner spiritual awakening. Now, it is always good to have rules for newbie to follow but it is a temporary roadmap to get on high ground of spirituality. We have lot of those folks even me in this category.
Same as today any writer can write about general majority of Sikhs being non-turbaned, drinking or some smoking. 100 years later we cannot simply believe that they were the actual Sikh. Just like in past there were actual Sikhs who followed guru path and some who were on and off that path with their weakness. Maharaja Ranjit is the perfect example of a Sikh who was not a Sikh in our guru eyes with his lifestyle.