Would you rather want to wait till marriage to intimately know your partner or will you rather know everything there is before marriage?
From a religious perspective, I think that sex should definitely be done after marriage. Marriage is not just about having sex, it is about mutual responsibility, understanding, and trusting each other. A marriage cannot be sustained by sex alone, happiness will come in life if a good relationship is developed between the two.
If you are religious and your religion does not allow you to have sex before marriage, you need to comply.
Sex is not the only factor to maintain marriage and many other factors are needed. But as a married person and from what my friends have shared, I think sex plays a very important role in bringing happiness to couples.
It can be said that sex will help couples be happier and increase emotional attachment. Besides, it also helps us reduce stress, anxiety and brings mental health. It's no coincidence that sex is called "the best natural happiness medicine"
Personally, I do not believe that any marriage can be happy and lasting without sex.