Why do Torah marriages work [if done correctly] and non-Torah marriages all too often don't work?
Non-Torah marriages are based on "love". "Love" is beautiful. It is the BEST. It is the sugar and spice of life. We can wax so poetic about love and not scratch the surface. The only problem is that LOVE IS FLEETING. Here today, gone .... at some unknown point in the future [or the next time the guy sees a pretty girl walking down the street or on the screen or the girl gets offended by something he did or didn't do].
According to the Torah, marriage is NOT about love - at least not at the outset. Marriage is a financial agreement. Learn all the masechtos that talk about marriage and nary a word about love. Here is the crux of the issue. The man is OBLIGATED to the woman. The woman is OBLIGATED to the man. It is IRRELEVANT whether they feel love or not. Sexual relations are a religious obligation. One may forgo it as one may forgo keeping Shabbos or eating kosher. Financial support is an obligation. Buying presents is an obligation [at least every yom tov]. Cooking and cleaning are obligations. Lots and lots of obligations.
AFTER both sides are fully committed to fulfilling their obligations regardless of the circumstances, then we hope a deep love will slowly develop. It takes time, hard work, patience, good will and dedication.
When it happens it is the best - and it lasts.
Does everybody do it right? No. Do most people do it right? No. But you can be the exception and be exceptional.
Hatzlacha!