In relationships where the woman is 15-25 years younger than the man, it is a common problem, that the gentleman gets to feel more like a father for his younger lady, as opposed to a partner. Relationships with such an age difference that go on for many years can lead to changes in the role of the male partner.
The typical role model of man and woman in a relationship is that the man is the strong part, bringing home the money, being the shoulder to lean on to and providing safety and security to his wife. This role is even strengthened when the man is much older than the woman. Big age differences can cause generation gaps and a lack of mutual interests. Sometimes these problems come step by step and mostly unnoticed.
The love life is decreasing, the younger woman sees her partner more and more like a provider and protector. He might lose interest in leading an active and sociable life and so what once was a spicy romance becomes a trustful friendship.
None of the partners, neither the younger ladies nor the older gentlemen can be blamed for this development. It is something that age difference might automatically bring about. The older man finds himself in a role he did not plan. He takes care of his younger wife or girlfriend and because he is much more experienced than her in some ways, it can quickly happen that he starts acting a bit bossy or smart-aleck. One thing leads to another and soon he acts like her father and not as her lover anymore. Likewise, the younger woman starts seeing her older partner more like a father figure than a partner.
By the same token, some younger women suffer from a psychological weakness, the so called father complex. Those ladies probably had a lack of a father figure in their lives and try to replace that loss with a partner they can also see a father in. The older gentleman has to keep that in mind as a possible reason for her behavior. A relationship like that can also mean a mutual benefit. Some partners consciously decide to lead partnerships with this certain role allocation. It can be a relationship of giving and taking. The older gentleman can take advantage of the fact that he is a strong shoulder for his partner and the younger lady can enjoy a life with someone who guides her and shows her things in life that she did not know before.
Romance and sexual affection are values that need to be kept safe like a precious treasure. They have to be nourished and maintained in order not to get lost along the way of a long term relationship. Both partners have to make an effort not to fall into the trap where the fine line between father figure and lover vanishes.