Firstly, these are numerous variations of the type “I love - they don't love me” or “they love me - I don't love”. Probably, they are most of all - because of the natural aggression and acquired envy, greed, touchiness, and psychotrauma. Do not believe it - take a look at the assortment of shelves of any medium bookstore. Is this law or the will of chance? I think that neither one nor the other. Just what kind of person is crooked - and his love sometimes is like a reproduction of a lonely Japanese pine. Or, as the French proverb says: "Let every shit look for its own shit." Although I prefer the answer: “If you doubt, it means you don't love” ... Ask any normal parent. If that is near an army of books, at your service there are consultations of psychologists and psychotherapists (there are also free ones in state institutions), pharmacies headed by Her Majesty Seti ...
Although there is nothing in this, I think, nothing so terribly reprehensible if a person allows another to love himself as an addition - due to the fact that he does not have any qualities, knowledge, skills, or even material objects that are peculiar to a loving person. Rich and unbalanced and poor with a harmonious character. An educated professional and skilled hostess with a TV instead of an iconostasis. “We use each other to fill empty places,” Grebenshchikov sang thirty years ago. Sometimes such alliances are even quite strong and long-term. Not one such know.
Secondly, the thesis that love is always mutual. Like the saints to the Most High. But this happens rarely even in the programs of Malakhov. Indeed, in contrast to the angel, who, though completely undoubtedly good or evil, performs unconditionally the will of his master, he differs little from a computer program. Man is a more multifaceted creature. He has: body and soul, gender, and most importantly - free will. Time sharpens the metal, the stone, and change a person to him - just spit. And thank you, that it is still so indulgent to us: now marriage in Russia exists on average 7 years, and I don’t think that love is longer. The luggage of past relationships, the trash of prejudice, the shackles of the rules, is not an easy burden. Even the fact that a loved one always pulls - very energy-intensive, because this force of attraction is not weaker than gravity. That is why almost any love and obstacles can overcome. And the word itself is rarely used by true lovers - it's like sitting by the river and selling water.
There are those who believe that they need to become “better” for someone to love them. And some teach that in love there can be no patience or reasoning about what you like or don't like in a person. But after all, any person usually wants to be loved. I know a lot of people who grew up in rejection and neglect, and to accuse them of inappropriate behavior is a big mistake. And what's so bad about self-improvement? Only that a person wants to love him, and not himself. And to start with yourself, even in this it is necessary.
By the way, the strongest and friendliest couples that I saw were distinguished by one interesting quality - rather frequent grumbling without anger and criticism without aggression. Just a man - a rhythmic being. In the body, it is respiration, heartbeat, food cycle, sexual rhythms (same monthly). Outside the body, these are natural, like a sine wave, mood swings, activity, performance. They do not coincide in people initially. However, it has been proven that with a long life together, their mutual “synchronization”, habituation, occurs. But until that happens, you don’t have to wait for 7 or some years. Understanding - this is observation, and feeling, and questions, and knowing when it is better not to disturb the lover once again. And you can start right away.
Absolutely everyone (a sick, poor, illiterate ...) person is able to love. If you still have not found this, then the main obstacle is inattention to yourself. It can be changed, then we and the people. Then you can hear and do what the heart says. This will be the path to happiness.