Most couple seeme to be happy before marriage but relationship strains post marriage? Can anyone explain what causes that

Expectations change, before marriage you are carefree and after marriage you have to meet expectations and your expectations also have to be met. Any disconnect can cause strain in your relationship. Only relationships work where One is a submissive and the other dominant. Now when both want to be dominant, conflicts happen and relationships deteriorate. Not having enough Sex is one of the main reasons.

Responsibility and reality