In general terms, in family psychology, almost any discomfort in a couple's relationship that lasts a certain period of time can be attributed to the crisis of family life.
Sometimes the crisis goes unnoticed even for the spouses themselves, and all they can say about it later is (approximately) that they began to devote less time to each other, maybe they got carried away with ordinary life.
The other extreme of the crisis is a stormy showdown with cries and impulses to break the union and equally expressive reconciliations. But usually everything happens between these two poles, in the average version.
As a rule, a crisis never comes from a single reason. Its emergence and development is based on many factors, some of which are dominant, others are concomitant, and others are present in a light shadow. They can both maintain a stable position and change, that is, come to the fore, or lose their significance as the crisis progresses.

Usually these reasons include:

Financial difficulties. Manifested in the form of a lack of money for the most necessary (food, seasonal clothes, utility bills, medicines), unjustified hopes of one side for material support for the second half, loans (rightly creating a feeling of a trap), disputes about the overall budget (when one earns more and wants to have decisive vote).

Lack of personal time. If work and, in particular, family obligations deprive a person of the opportunity to take care of himself, engage in self-development, devote time to hobbies, it is natural for him to experience chronic fatigue, apathy and irritation at the reason that led to this, that is, at his soulmate.

Birth of a child. In this case, one of the partners (usually the husband) may feel jealous - for the love and attention, care and time devoted to the baby. The couple may also be at odds over the upbringing and care of the child.

Everyday life and everyday life. It may seem surprising, but what is usually considered a normal, familiar, calm course of life for a person is a serious test for love relationships. After all, the two in this have to share responsibilities, contribute and find options for thousands of solutions that should suit both (even the timing of breakfast in the family can become a problem). Plus, all this shows a loved one not from a fabulous, romantic side, but from the most ordinary. And, willy-nilly, you have to look for what else you can love him for, in addition to those features that turned your head at first.

Big problems. This can be a serious illness, business problems, and much more, which puts one of the partners in a weaker, more vulnerable position, when a person is in dire need of emotional and practical support, care and empathy. Plus, many problems not only exist nearby, but also affect the soulmate, which can also cause discontent.