One may say that marriage signifies fidelity, commitment and responsibility. To have an extramarital affair may eventually lead to a breakdown of the family. This can have dare consequences (both financial and emotional). It just may be too dear to have an inamorata or inamorato dehors the marriage. It's a completely different story if you're a single or a divorcé(e), and you can definitively say "hey, this is a free country". Enjoy that freedom while you can!
If you like sth in shopping centre, and you just take it before it belong to you, that is 'steal'.
if you park your car anyplace you want, you will sure get a traffic ticket...
As a human being, you have to follow some rules or take some responsabilities.